Move the DMSAA surface flag into the public API

Bug: skia:11396
Change-Id: Iad175ea9727e0b18b94a7af341c831e03da46880
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/427484
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
8 files changed