Also adds flexibility to unpremul the input, clamp the output, premul the
output or not.
Also fixes SkMatrix44 as a ctype.
The intent is to reuse this for rgb->yuv conversion in async rescale and
read.
Bug: skia:3962
Change-Id: I470d1cfebdbd79d8541b633c1747d510a5549ac4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/217128
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
