Update SkModeColorFilter to support an input FP.

This change relies on the Xfermode updates in the prior CL
(http://review.skia.org/299703) to render properly, and requires
slightly different blending behavior in the compose FP which
necessitated a new ComposeBehavior enum.

Eventually we would like to settle on a universal ComposeBehavior which
works well for all call sites, but that will be its own fairly
disruptive change. This work will be tracked at skia:10457.

Change-Id: I3cc0ea5e016fbef82bc63d653d60d0505efaa66f
Bug: skia:10217
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/298821
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
7 files changed