Simplify masked stores when the execution mask is known.

We can replace any masked store with an unmasked store if we know
that the mask is all-true.

Change-Id: Ie418cdbbec0970b095ccf6385458a6503d41f44b
Bug: skia:13676
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/632616
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
149 files changed