Optimize SkSL xor where one argument is constant

Change-Id: I9ea41625fd80433f7f6480fe539321d8df7b7930
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/258877
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
3 files changed