[skottie] Add support for opacity text animators

Change-Id: I76da8745ccd714cb8457000d9cd208e62f1058ba
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/217536
Auto-Submit: Florin Malita <fmalita@chromium.org>
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
1 file changed