Revert "Make FP optimizations helpers use SkAlphaType not GrColorType"

This reverts commit 7a538b1eeccdbe940de507af9aeaf454952c4aec.

Reason for revert: ios failures

Original change's description:
> Make FP optimizations helpers use SkAlphaType not GrColorType
> 
> Change-Id: I3b7cde6e7f68192af5419fb09c7d59e7a803a4d5
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/255818
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Greg Daniel <egdaniel@google.com>

TBR=egdaniel@google.com,bsalomon@google.com

Change-Id: Id41daa47fb3ccac434bb9d71a697f32e36c87367
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/255835
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
58 files changed