hide hinting and flag enums with PAINT_FLAGS

A preflight for https://skia-review.googlesource.com/c/skia/+/185460

Bug: skia:2664
Change-Id: I83f7f9cd500e8507b559462835477ba8ae7c11ab
Reviewed-on: https://skia-review.googlesource.com/c/185540
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Auto-Submit: Mike Reed <reed@google.com>
5 files changed