add plumbing for color filter SkSL effect

Change-Id: I26b28ff4756cda921e4acef32f3da3b43b1fc28f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/472936
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Jorge Betancourt <jmbetancourt@google.com>
4 files changed