Add optional form for SkRRect::transform()

... in preparation for new impl of transform itself
see https://skia-review.googlesource.com/c/skia/+/1029976

Change-Id: I3c7c206933b24e52925833ed125f88da8a0e6610
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1029919
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Mike Reed <mike@reedtribe.org>
Reviewed-by: Eric Boren <borenet@google.com>
16 files changed