Setup support for UNIFORM_TEXEL_BUFFER descriptor sets in Vulkan

This is the first CL to get support for using texel buffers in vulkan.

Bug: skia:
Change-Id: Iaac5ba4a356b487bc2b63111cca34ed968881f6b
Reviewed-on: https://skia-review.googlesource.com/15100
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
7 files changed