Work on hiding filter-quality

SkPaintPriv methods are just an internal stopgap

Change-Id: Ibe6e37c5871068d8cd67dc0948961444dfd2b62a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/347041
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
12 files changed