Remove all remaining GrColor4f (other than gradients)

This adds SkPMColor4f conversions to/from RGBA bytes (ie GrColor).
I had previously made some free functions that did the same thing.
I'm ambivalent about which option is nicer, but wanted to have one
method, so I converted everything to use the new versions.

Bug: skia:
Change-Id: I4194c44b5bd12228075fd1932a14cf31c8d6a3c1
Reviewed-on: https://skia-review.googlesource.com/c/162560
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
27 files changed