[graphite] Use SkSpan for YUVATextureProxies and YUVABackendTextures.

This allows clients to use whatever array structure they like for
their input data.

Bug: b/285361134
Change-Id: Ie804c36c727eaf85bd3c49d6da6553286d309db2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/708393
Reviewed-by: Florin Malita <fmalita@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
5 files changed