[graphite-dawn] Implement read pixels' support

Bug: b/266166822
Change-Id: I526c5b1b883b8d7c45a589d84f70e7d06672c372
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/632136
Reviewed-by: Nicolette Prevost <nicolettep@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
4 files changed