[skottie] Cleanup: split animators into separate CUs

No functional changes, just code reshuffle.

TBR=

Change-Id: Ia04add9d51d6e84903d010534434c9a60464a72a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/277457
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
23 files changed