Reland "asyncRescaleAndRead supports unpremul results on GPU"

This is a reland of 70fa84a9bf506dcb3b4e78e32f28d3d2b521893a

Bug: skia:11019

Original change's description:
> asyncRescaleAndRead supports unpremul results on GPU
>
> GrSurfaceContext::rescale uses GrSurfaceFillContext instead of
> GrSurfaceDrawContext.
> Change-Id: I9c2d647d8f221c129ec4485a4ed936202aee6362
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/351923
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> Commit-Queue: Brian Salomon <bsalomon@google.com>

Cq-Include-Trybots: luci.chromium.try:android-marshmallow-arm64-rel
Change-Id: I7b696c37edea8f755ec03431d026ea78556e5844
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/353099
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
10 files changed