Introduce GrColorType

This begins the journey towards using different types to refer to CPU data and GPU texture formats. This is one part of removing GrPixelConfig and more directly using GL/VK texture formats

GrColorType represents a particular layout of color/gray/alpha channels in CPU memory. It does not refer to texture formats or sRGB-encoding. It is basically SkColorType specialized to the GPU backend with some formats added and some removed.

Read/WritePixel interfaces use GrColorType to describe the CPU side of the transaction.

There's still a lot of punting to GrPixelConfig in API-specific code. There's a lot more to be done.

Bug: 6718
Bug: 7580

Change-Id: I8d813ae9a4416a06596f22a4b87da02091989718
Reviewed-on: https://skia-review.googlesource.com/107264
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
20 files changed