Introduce new factory for SkColorFilters

Idea: transition callers to this, so we can later typedef SkColorFilter
and SkShader to the same thing.

Bug: skia:8937
Change-Id: I000c882e11622091aa44c141aa6ddd1216414f46
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/206685
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Reed <reed@google.com>
64 files changed