Move runtime shader/colorfilter into SkRuntimeEffect.cpp

Better organization that lets us share a bunch of code between these
(very similar) objects.

Change-Id: Ie559d6e144d8588b98a95d4170e2e6c19d9623bd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/270736
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
7 files changed