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

This reverts commit 97ae0c89025dfd791047f5701e57d58da37c125c.

Reason for revert: Breaking ANGLE.

Original change's description:
> 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>

TBR=bsalomon@google.com,robertphillips@google.com,ethannicholas@google.com

Change-Id: I65d6d2707fceab0a99121c528d1b848d23e34bfa
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/142588
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
83 files changed