Enable vertex ID support on Metal

This allows the tessellated stroke renderer to run on Metal.

Change-Id: Ia6bd4008a3310cd316abdc2715efcec3916c6bfa
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/408358
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/mtl/GrMtlCaps.mm b/src/gpu/mtl/GrMtlCaps.mm
index b767c05..486f046 100644
--- a/src/gpu/mtl/GrMtlCaps.mm
+++ b/src/gpu/mtl/GrMtlCaps.mm
@@ -473,7 +473,7 @@
 
     shaderCaps->fIntegerSupport = true;
     shaderCaps->fNonsquareMatrixSupport = true;
-    shaderCaps->fVertexIDSupport = false;
+    shaderCaps->fVertexIDSupport = true;
 
     // Metal uses IEEE float and half floats so assuming those values here.
     shaderCaps->fFloatIs32Bits = true;