[rust png] Implement `SkPngRustCodec::onGetRepetitionCount`.

This CL exposes `png::AnimationControl` over FFI, and then uses it to
implement `SkPngRustCodec::onGetRepetitionCount`.  After this CL, the
`RustEnabled/AnimatedPNGTests.repetitionCountTest/0` test starts to pass
(after patching in https://crrev.com/c/5786777 in Chromium).

Bug: chromium:356922876
Change-Id: I2e4b010609f31a860f6356b7552376d84f5d106f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/897176
Auto-Submit: Ɓukasz Anforowicz <lukasza@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed