[canvaskit] Add docs/types for Skottie and Particles

This should be it. Caught up with 0.18.0

Change-Id: Ibe846d756601e42e315ab510807abd4bbd9cf30d
Bug: skia:10717
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/322323
Reviewed-by: Kevin Lubick <kjlubick@google.com>
2 files changed