Rename gl_SampleMask to sk_SampleMask

Change-Id: I3924c6f76edf310a984e4fd89478b00eeec69722
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249931
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
7 files changed