[graphite] Add support for Mtl Stencil/Depth Textures.

Bug: skia:12466
Change-Id: I38f3469c53414c36b05f3bdbc266b50783cfa676
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/455496
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
3 files changed