AnimationGraph for AnimationPlayers

[ChristopherBiscardi]

Many users wish to have a simpler animation integration. I've mostly put this off because its possible to do without skein, but things like animation events firing might not be and are worth exploring.

minimum version would be something like trying to track all of the actions in an animation that turns into the node with the AnimationPlayer on it, and setting them up to also have the AnimationGraph with each animation individually. This must be either opt-in or opt-out; ie: it can't ship if it applies to everything all the time and the user can't disable it.

making it opt-in might be nice for future more advanced animationgraph work.

[ChristopherBiscardi]

I added an example upstream that can use gltf extension handlers to create animation graphs. IMO this is probably a good quality of life improvement in animation UX at least for users who mainly use single animations at a time. Maybe we could also build more native integration against actions/etc so a user wouldn't have to label them explicitly.

https://github.com/bevyengine/bevy/blob/bb23d0d76ac2843cad59c205606c71286d6eab19/examples/gltf/gltf_extension_animation_graph.rs