sksl enum support

Bug: skia:
Change-Id: I4d505b31cf8b59de12bcdbca410aafc085977ba9
Reviewed-on: https://skia-review.googlesource.com/68621
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
47 files changed