Reland "Revert "Revert "Make FP optimizations helpers use SkAlphaType not GrColorType"""

This is a reland of 997b37fdb986b45ff9941319b0111b188e749cfc

Layout tests have been suppressed.

Original change's description:
> Revert "Revert "Make FP optimizations helpers use SkAlphaType not GrColorType""
>
> This reverts commit 078e8faa26d8b1f33a92e57f587be011150d1776.
>
> Change-Id: I67b2970584db5a1afbf9928b77c5444947ef71a3
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/255897
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Salomon <bsalomon@google.com>

Change-Id: I6db4cff8b71ef1f29ac47f7729b9514d009f730a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/256225
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
59 files changed