Add support for VK_KHR_separate_depth_stencil_layouts extension.

Add VK_KHR_separate_depth_stencil_layouts and enable its features.
Metal generally ignores image layouts, so nothing further needed.
Update Whats_New.md and MoltenVK_Runtime_UserGuide.md documents
with recently-added extensions.

Passes almost all supported separate_layouts CTS tests, with the
few remaining tests failing due to issues with unrelated capabilities.

Unrelated cleanup:
- MVKDevice enable extensions before features.
- MVKDevice reorder ivar declarations to reduce
  memory layout gaps, and define default values.
- Rename VkSemaphoreStyle to MVKSemaphoreStyle to
  remove potential conflicts with Vulkan Vk name space.
diff --git a/Docs/MoltenVK_Runtime_UserGuide.md b/Docs/MoltenVK_Runtime_UserGuide.md
index 2f87262..ca1c436 100644
--- a/Docs/MoltenVK_Runtime_UserGuide.md
+++ b/Docs/MoltenVK_Runtime_UserGuide.md
@@ -270,6 +270,7 @@
 - `VK_KHR_device_group`
 - `VK_KHR_device_group_creation`
 - `VK_KHR_driver_properties`
+- `VK_KHR_dynamic_rendering`
 - `VK_KHR_get_memory_requirements2`
 - `VK_KHR_get_physical_device_properties2`
 - `VK_KHR_get_surface_capabilities2`
@@ -284,6 +285,7 @@
 - `VK_KHR_relaxed_block_layout`
 - `VK_KHR_sampler_mirror_clamp_to_edge` *(requires a Mac GPU or Apple family 7 GPU)*
 - `VK_KHR_sampler_ycbcr_conversion`
+- `VK_KHR_separate_depth_stencil_layouts`
 - `VK_KHR_shader_draw_parameters`
 - `VK_KHR_shader_float16_int8`
 - `VK_KHR_shader_subgroup_extended_types` *(requires Metal 2.1 on Mac or Metal 2.2 and Apple family 4 on iOS)*
@@ -309,6 +311,7 @@
 - `VK_EXT_robustness2`
 - `VK_EXT_sample_locations`
 - `VK_EXT_scalar_block_layout`
+- `VK_EXT_separate_stencil_usage`
 - `VK_EXT_shader_stencil_export` *(requires Mac GPU family 2 or iOS GPU family 5)*
 - `VK_EXT_shader_viewport_index_layer`
 - `VK_EXT_subgroup_size_control` *(requires Metal 2.1 on Mac or Metal 2.2 and Apple family 4 on iOS)*
diff --git a/Docs/Whats_New.md b/Docs/Whats_New.md
index 2718328..3e11894 100644
--- a/Docs/Whats_New.md
+++ b/Docs/Whats_New.md
@@ -23,6 +23,7 @@
 	  updated to indicate the impact of the `VK_KHR_portability_enumeration` extension during 
 	  runtime loading on *macOS* via the *Vulkan Loader*.
 	- `VK_KHR_dynamic_rendering`
+	- `VK_KHR_separate_depth_stencil_layouts`
 	- `VK_EXT_separate_stencil_usage`
 - Fix error where previously bound push constants can override a descriptor buffer binding 
   used by a subsequent pipeline that does not use push constants.
diff --git a/MoltenVK/MoltenVK/GPUObjects/MVKDevice.h b/MoltenVK/MoltenVK/GPUObjects/MVKDevice.h
index 42804ed..63b6e18 100644
--- a/MoltenVK/MoltenVK/GPUObjects/MVKDevice.h
+++ b/MoltenVK/MoltenVK/GPUObjects/MVKDevice.h
@@ -429,6 +429,12 @@
 	id<MTLCommandBuffer> mtlCmdBuffer = nil;
 } MVKMTLBlitEncoder;
 
+typedef enum {
+	MVKSemaphoreStyleUseMTLEvent,
+	MVKSemaphoreStyleUseMTLFence,
+	MVKSemaphoreStyleUseEmulation
+} MVKSemaphoreStyle;
+
 /** Represents a Vulkan logical GPU device, associated with a physical device. */
 class MVKDevice : public MVKDispatchableVulkanAPIObject {
 
@@ -762,6 +768,9 @@
 
 #pragma mark Properties directly accessible
 
+	/** The list of Vulkan extensions, indicating whether each has been enabled by the app for this device. */
+	const MVKExtensionList _enabledExtensions;
+
 	/** Device features available and enabled. */
 	const VkPhysicalDeviceFeatures _enabledFeatures;
 	const VkPhysicalDevice16BitStorageFeatures _enabledStorage16Features;
@@ -781,9 +790,7 @@
 	const VkPhysicalDevicePortabilitySubsetFeaturesKHR _enabledPortabilityFeatures;
 	const VkPhysicalDeviceImagelessFramebufferFeaturesKHR _enabledImagelessFramebufferFeatures;
 	const VkPhysicalDeviceDynamicRenderingFeatures _enabledDynamicRenderingFeatures;
-
-	/** The list of Vulkan extensions, indicating whether each has been enabled by the app for this device. */
-	const MVKExtensionList _enabledExtensions;
+	const VkPhysicalDeviceSeparateDepthStencilLayoutsFeatures _enabledSeparateDepthStencilLayoutsFeatures;
 
 	/** Pointer to the Metal-specific features of the underlying physical device. */
 	const MVKPhysicalDeviceMetalFeatures* _pMetalFeatures;
@@ -858,21 +865,15 @@
 	std::mutex _rezLock;
 	std::mutex _sem4Lock;
     std::mutex _perfLock;
-    id<MTLBuffer> _globalVisibilityResultMTLBuffer;
-	id<MTLSamplerState> _defaultMTLSamplerState;
-	id<MTLBuffer> _dummyBlitMTLBuffer;
-    uint32_t _globalVisibilityQueryCount;
-    std::mutex _vizLock;
-	bool _logActivityPerformanceInline;
-	bool _isPerformanceTracking;
-	bool _isCurrentlyAutoGPUCapturing;
-
-	typedef enum {
-		VkSemaphoreStyleUseMTLEvent,
-		VkSemaphoreStyleUseMTLFence,
-		VkSemaphoreStyleUseEmulation
-	} VkSemaphoreStyle;
-	VkSemaphoreStyle _vkSemaphoreStyle;
+	std::mutex _vizLock;
+    id<MTLBuffer> _globalVisibilityResultMTLBuffer = nil;
+	id<MTLSamplerState> _defaultMTLSamplerState = nil;
+	id<MTLBuffer> _dummyBlitMTLBuffer = nil;
+	MVKSemaphoreStyle _vkSemaphoreStyle = MVKSemaphoreStyleUseEmulation;
+    uint32_t _globalVisibilityQueryCount = 0;
+	bool _logActivityPerformanceInline = false;
+	bool _isPerformanceTracking = false;
+	bool _isCurrentlyAutoGPUCapturing = false;
 
 };
 
diff --git a/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm b/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm
index 520a464..88ef958 100644
--- a/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm
+++ b/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm
@@ -282,6 +282,11 @@
 				dynamicRenderingFeatures->dynamicRendering = true;
 				break;
 			}
+			case VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_SEPARATE_DEPTH_STENCIL_LAYOUTS_FEATURES: {
+				auto* separateDepthStencilLayoutsFeatures = (VkPhysicalDeviceSeparateDepthStencilLayoutsFeatures*)next;
+				separateDepthStencilLayoutsFeatures->separateDepthStencilLayouts = true;
+				break;
+			}
 			default:
 				break;
 		}
@@ -3327,9 +3332,9 @@
 		}
 	} else {
 		switch (_vkSemaphoreStyle) {
-			case VkSemaphoreStyleUseMTLEvent:  return new MVKSemaphoreMTLEvent(this, pCreateInfo);
-			case VkSemaphoreStyleUseMTLFence:  return new MVKSemaphoreMTLFence(this, pCreateInfo);
-			case VkSemaphoreStyleUseEmulation: return new MVKSemaphoreEmulated(this, pCreateInfo);
+			case MVKSemaphoreStyleUseMTLEvent:  return new MVKSemaphoreMTLEvent(this, pCreateInfo);
+			case MVKSemaphoreStyleUseMTLFence:  return new MVKSemaphoreMTLFence(this, pCreateInfo);
+			case MVKSemaphoreStyleUseEmulation: return new MVKSemaphoreEmulated(this, pCreateInfo);
 		}
 	}
 }
@@ -3981,10 +3986,10 @@
 	_enabledPortabilityFeatures(),
 	_enabledImagelessFramebufferFeatures(),
 	_enabledDynamicRenderingFeatures(),
-	_enabledExtensions(this),
-	_isCurrentlyAutoGPUCapturing(false)
-{
-	// If the physical device is lost, bail.
+	_enabledSeparateDepthStencilLayoutsFeatures(),
+	_enabledExtensions(this) {
+
+		// If the physical device is lost, bail.
 	if (physicalDevice->getConfigurationResult() != VK_SUCCESS) {
 		setConfigurationResult(physicalDevice->getConfigurationResult());
 		return;
@@ -3992,8 +3997,8 @@
 
 	initPerformanceTracking();
 	initPhysicalDevice(physicalDevice, pCreateInfo);
-	enableFeatures(pCreateInfo);
 	enableExtensions(pCreateInfo);
+	enableFeatures(pCreateInfo);
 	initQueues(pCreateInfo);
 	reservePrivateData(pCreateInfo);
 
@@ -4075,15 +4080,15 @@
 	bool isRosetta2 = _pProperties->vendorID == kAppleVendorId && !MVK_APPLE_SILICON;
 	bool canUseMTLEventForSem4 = _pMetalFeatures->events && mvkConfig().semaphoreUseMTLEvent && !(isRosetta2 || isNVIDIA);
 	bool canUseMTLFenceForSem4 = _pMetalFeatures->fences && mvkConfig().semaphoreUseMTLFence;
-	_vkSemaphoreStyle = canUseMTLEventForSem4 ? VkSemaphoreStyleUseMTLEvent : (canUseMTLFenceForSem4 ? VkSemaphoreStyleUseMTLFence : VkSemaphoreStyleUseEmulation);
+	_vkSemaphoreStyle = canUseMTLEventForSem4 ? MVKSemaphoreStyleUseMTLEvent : (canUseMTLFenceForSem4 ? MVKSemaphoreStyleUseMTLFence : MVKSemaphoreStyleUseEmulation);
 	switch (_vkSemaphoreStyle) {
-		case VkSemaphoreStyleUseMTLEvent:
+		case MVKSemaphoreStyleUseMTLEvent:
 			MVKLogInfo("Using MTLEvent for Vulkan semaphores.");
 			break;
-		case VkSemaphoreStyleUseMTLFence:
+		case MVKSemaphoreStyleUseMTLFence:
 			MVKLogInfo("Using MTLFence for Vulkan semaphores.");
 			break;
-		case VkSemaphoreStyleUseEmulation:
+		case MVKSemaphoreStyleUseEmulation:
 			MVKLogInfo("Using emulation for Vulkan semaphores.");
 			break;
 	}
@@ -4110,10 +4115,15 @@
 	mvkClear(&_enabledPortabilityFeatures);
 	mvkClear(&_enabledImagelessFramebufferFeatures);
 	mvkClear(&_enabledDynamicRenderingFeatures);
+	mvkClear(&_enabledSeparateDepthStencilLayoutsFeatures);
+
+	VkPhysicalDeviceSeparateDepthStencilLayoutsFeatures pdSeparateDepthStencilLayoutsFeatures;
+	pdSeparateDepthStencilLayoutsFeatures.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_SEPARATE_DEPTH_STENCIL_LAYOUTS_FEATURES;
+	pdSeparateDepthStencilLayoutsFeatures.pNext = nullptr;
 
 	VkPhysicalDeviceDynamicRenderingFeatures pdDynamicRenderingFeatures;
 	pdDynamicRenderingFeatures.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_DYNAMIC_RENDERING_FEATURES;
-	pdDynamicRenderingFeatures.pNext = NULL;
+	pdDynamicRenderingFeatures.pNext = &pdSeparateDepthStencilLayoutsFeatures;
 
 	VkPhysicalDeviceImagelessFramebufferFeaturesKHR pdImagelessFramebufferFeatures;
 	pdImagelessFramebufferFeatures.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_IMAGELESS_FRAMEBUFFER_FEATURES;
@@ -4321,6 +4331,13 @@
 							   &pdDynamicRenderingFeatures.dynamicRendering, 1);
 				break;
 			}
+			case VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_SEPARATE_DEPTH_STENCIL_LAYOUTS_FEATURES: {
+				auto* requestedFeatures = (VkPhysicalDeviceSeparateDepthStencilLayoutsFeatures*)next;
+				enableFeatures(&_enabledSeparateDepthStencilLayoutsFeatures.separateDepthStencilLayouts,
+							   &requestedFeatures->separateDepthStencilLayouts,
+							   &pdSeparateDepthStencilLayoutsFeatures.separateDepthStencilLayouts, 1);
+				break;
+			}
 			default:
 				break;
 		}
diff --git a/MoltenVK/MoltenVK/Layers/MVKExtensions.def b/MoltenVK/MoltenVK/Layers/MVKExtensions.def
index b0ae830..019b23b 100644
--- a/MoltenVK/MoltenVK/Layers/MVKExtensions.def
+++ b/MoltenVK/MoltenVK/Layers/MVKExtensions.def
@@ -72,6 +72,7 @@
 MVK_EXTENSION(KHR_relaxed_block_layout,            KHR_RELAXED_BLOCK_LAYOUT,             DEVICE,   10.11,  8.0)
 MVK_EXTENSION(KHR_sampler_mirror_clamp_to_edge,    KHR_SAMPLER_MIRROR_CLAMP_TO_EDGE,     DEVICE,   10.11, 14.0)
 MVK_EXTENSION(KHR_sampler_ycbcr_conversion,        KHR_SAMPLER_YCBCR_CONVERSION,         DEVICE,   10.11,  8.0)
+MVK_EXTENSION(KHR_separate_depth_stencil_layouts,  KHR_SEPARATE_DEPTH_STENCIL_LAYOUTS,   DEVICE,   10.11,  8.0)
 MVK_EXTENSION(KHR_shader_draw_parameters,          KHR_SHADER_DRAW_PARAMETERS,           DEVICE,   10.11,  8.0)
 MVK_EXTENSION(KHR_shader_float16_int8,             KHR_SHADER_FLOAT16_INT8,              DEVICE,   10.11,  8.0)
 MVK_EXTENSION(KHR_shader_subgroup_extended_types,  KHR_SHADER_SUBGROUP_EXTENDED_TYPES,   DEVICE,   10.14, 13.0)