RFR: 8324658: Allow animation play/start/stop/pause methods to be called on any thread [v16]

[Nir Lisker]

> Added a utility method to run code on the FX thread if it's not already, and changed the animation methods to use it.

Nir Lisker has updated the pull request incrementally with one additional commit since the last revision:

  Use AtomicReferences

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1352/files
  - new: https://git.openjdk.org/jfx/pull/1352/files/789b0f2f..13281050

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1352&range=15
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1352&range=14-15

  Stats: 6 lines in 1 file changed: 1 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jfx/pull/1352.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1352/head:pull/1352

PR: https://git.openjdk.org/jfx/pull/1352