onProgram for SkGaussianColorFilter, plus gm and bench

iMac Pro bench:
- RP:          167
- VM exp:      195
- VM quartics: 135

Change-Id: Ie8deb38f246b9ae7bbd35e59c3e7e66fc7c42de5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/279918
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Mike Reed <reed@google.com>
4 files changed