[graphite] Combine YUVA and regular promise image callbacks

Other than having the image context be the texture fulfill context for
non-YUVA promise images, the lazy callback logic was identical so this
moves the promise proxy creation into TextureUtils and uses a single
callback definition.

Bug: b/333909822
Change-Id: I68cf1d6b857d27062afc72c553c80c50409bd3c6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/838457
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
9 files changed