Experimental: Add R_16 and RG_1616 to Ganesh (take 2)

This is to support the P016 and P010 YUV formats. Initially, only Vulkan and GL support these formats.

Change-Id: I4e896f1d3fb32207227a755517ae5a00a58e6045
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/219403
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
22 files changed