[graphite] Add buffer setup for texture uploads

Takes the given texture data and destination rectangle, copies it into
a buffer, and stores the destination textureProxy, buffer, and
associated BufferTextureCopyData into an UploadCommand.

Bug: skia:12845
Change-Id: Icba8b9e56ac0d79083c54fe529bd7e35ddb6e23d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/505798
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
5 files changed