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

[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.

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Commit messages:
 - Remove whitespace
 - Remove whitespace
 - Run methods on the FX thread

Changes: https://git.openjdk.org/jfx/pull/1352/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1352&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324658
  Stats: 65 lines in 4 files changed: 34 ins; 19 del; 12 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