Remove all clamping to "valid" premultiplied colors

Previously, we were abundantly cautious about producing premultiplied
colors with RGB > A, when the color-type was normalized fixed-point.

I'm not seeing any evidence that code cares about that. If it does, I
suggest we fix the issue at the API border, or via dedicated pass. In
the common case, this makes Skia less opinionated, which (in general)
makes it more versatile.

Change-Id: Iae524ff61f6c81073c34d0f2dced973c229cdfb7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/452558
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
4 files changed