Enforce extra constraints for mixed samples at GrCaps level

Change-Id: Icbeafeb25614d66e548027e5777ea1699d1e6f7d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/254116
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
8 files changed