De-namespace uses of MaskFormat

Bug: skia:13118
Change-Id: Iab67fd1148182fdd29a38b69f27c51b13942a2b5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/532400
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
14 files changed