[androidkit] Add an extra Skottie sample to CubeActivity

Also update SkottieSample to always clear its dest rect (for animations
which are not opaque).

Change-Id: I36c6172d468567ee8e03d97dd707e03ca968aa26
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/414898
Commit-Queue: Florin Malita <fmalita@google.com>
Reviewed-by: Jorge Betancourt <jmbetancourt@google.com>
3 files changed