Add support for immuatable samplers in vulkan.

For ycbcr conversions we need add immutable samplers to the creation of
the VkPipeline via the descriptor set layout.

Bug: skia:
Change-Id: I5eea6037191fd34d26d49f58533035316158cacd
Reviewed-on: https://skia-review.googlesource.com/c/171642
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
22 files changed