[graphite] Add ContextOptions override for Graphite (in dm)

This just adds the framework. A follow on CL will update the GMs to use the new code path.

Change-Id: I411148e44e471842a6067a22114a4b691f7fc2a0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/714060
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
13 files changed