added SkSL support for all blend mode layouts

Bug: skia:
Change-Id: Id39c068b15d0ae51520dc2169cdbf21402a43f69
Reviewed-on: https://skia-review.googlesource.com/76200
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
7 files changed