Revert "Revert "added GrSkSLFP and converted DitherEffect to use it""

This reverts commit f2030783094e502fb74221077a5ee7cb41287fe4.

Bug: skia:
Change-Id: Icaaa8b3ea652a8f126bfbcc788a360493a7ebe3e
Reviewed-on: https://skia-review.googlesource.com/137391
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
83 files changed