Allow animation play/start/stop/pause methods to be called on any thread

JavaFX Animations run on the JavaFX Application Thread. In JavaFX 21 and earlier, no checking was done in the Animation and AnimationTImer methods that start or stop an animation. Program that called these methods on a background thread -- especially the stop method -- ran into intermittent, hard-to-diagnose failures.

JDK-8159048, implemented earlier in the JavaFX 22 release, restricted the following methods to be called on the JavaFX Application Thread:

Animation:
  play
  pause
  stop

AnimationTimer
  start
  stop

Since implementing that approach we have become aware of compatibility issues where applications that create a timeline as part of a scene graph on a background thread start playing that animation by calling play on that same background thread. Those applications would largely run without problems as long as they didn't also call pause or stop on the background thread.

This RFE proposes a solution that avoids the threading problems that existed prior to JavaFX 22 without introducing the compatibility problems that the threading restriction implemented in JDK-8159048 caused.

The solution will be to document that the methods in question can be called on any thread, and that the implementation of those methods will be ensure that they are run on the JavaFX application thread. The implementation will then check the thread and wrap the implementation in a runLater if not already on the JavaFX application thread.