Create a GrGpu::createBackendTexture choke point

This also makes createBackendTexture take SkPixmaps (instead of a raw pixels pointer)

Change-Id: I5d8a5a58fa7b15862fbf46a3c232cb6ea7f58976
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/243158
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
11 files changed