[graphite] Add stubs for new Graphite-specific SkImage::makeSubset API

Bug: b/237111152
Change-Id: I2e15713fcde79dfca9075e300e74d39e65a4bbb1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/629916
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
10 files changed