RFR: 8343956: Focus delegation API

[Michael Strauß]

Implementation of [focus delegation](https://gist.github.com/mstr2/44d94f0bd5b5c030e26a47103063aa29).

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Commit messages:
 - javadoc
 - Added documentation
 - Add EventTarget.dispatchEvent(Event)
 - Capture (parent, delegate, dispatcher) in DelegatingEventDispatcher
 - Improved documentation, updated copyright headers
 - Merge branch 'master' into feature/focus-delegation
 - added getFocusDelegate(hoistingNode) parameter
 - Merge branch 'master' into feature/focus-delegation
 - Merge branch 'master' into feature/focus-delegation
 - added tests
 - ... and 3 more: https://git.openjdk.org/jfx/compare/0270847b...a9e6b8f8

Changes: https://git.openjdk.org/jfx/pull/1632/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1632&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343956
  Stats: 1045 lines in 16 files changed: 819 ins; 111 del; 115 mod
  Patch: https://git.openjdk.org/jfx/pull/1632.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1632/head:pull/1632

PR: https://git.openjdk.org/jfx/pull/1632