First implementation of GrDawnTexture.

Change-Id: I9c636c939dffbb0b395f3e9ed3d9a55784a6d390
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/233981
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>
9 files changed