RFR: 8358255: Factor out boilerplate code of EventHandler properties in Scene and Window

[Michael Strauß]

`EventHandler` property implementations in `Scene` and `Window` use anonymous classes derived from `ObjectPropertyBase`. We can remove about 650 lines of boilerplate code by using a common property class instead.

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Commit messages:
 - use EventHandlerProperty

Changes: https://git.openjdk.org/jfx/pull/1819/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1819&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358255
  Stats: 793 lines in 2 files changed: 50 ins; 694 del; 49 mod
  Patch: https://git.openjdk.org/jfx/pull/1819.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1819/head:pull/1819

PR: https://git.openjdk.org/jfx/pull/1819