[SkottieView] surface methods for  adding and removing listeners in SkottieView

Change-Id: Iaa97a5661269c9f725cf44f977fed12c3c994b31
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/375070
Reviewed-by: Stan Iliev <stani@google.com>
Commit-Queue: Stan Iliev <stani@google.com>
1 file changed