implement and test basic playback features for SkottieView

Change-Id: I46a673b2070d523cd9952179c56461fa61c4c5b8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/302036
Commit-Queue: Jorge Betancourt <jmbetancourt@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
6 files changed