Merge GrVkVertexBuffer and GrVkIndexBuffer into GrVkMeshBuffer

Change-Id: Icce3f3dce8581ba1ac3817d62c18e93cee616d3c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/281379
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
11 files changed