Enums are an SkSL-only concept--when we output code, we emit plain
IntLiterals--so the fix is simply to ignore the Enum program element
when we encounter it. This is what GLSLCodeGen does as well.
Also added a unit test to confirm that enums work normally, and that
enums are subject to optimization and static-comparison checks just as
ints would be.
Change-Id: Ic4f8da7a27983add9eb41b936d46f6638d22bd4b
Bug: skia:11003
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/338800
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
