Add SkSurface flush call that takes a GrBackendSurfaceMutableState.

This new api will eventually replace the version that takes an

SkSurface::BackendAccess.
Change-Id: I48cd013725e14027f386b0b111223459944ac44a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/295567
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
26 files changed