RFR: 8268225: Support :focus-visible and :focus-within CSS pseudoclasses

[Michael Strauß]

This PR adds the `Node.focusVisible` and `Node.focusWithin` properties, as well as the corresponding `:focus-visible` and `:focus-within` CSS pseudo-classes.

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Commit messages:
 - remove code comment
 - revert changes to line endings
 - added test
 - Merge branch 'master' into feature/focusvisible
 - Only fire focus change notification if value is actually different
 - minor naming change
 - added focusWithin
 - changed javadoc
 - Test for pseudo-class state
 - Changed javadoc, changed test
 - ... and 2 more: https://git.openjdk.java.net/jfx/compare/59cf4de3...7b3efd29

Changes: https://git.openjdk.java.net/jfx/pull/475/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=475&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268225
  Stats: 566 lines in 21 files changed: 415 ins; 35 del; 116 mod
  Patch: https://git.openjdk.java.net/jfx/pull/475.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/475/head:pull/475

PR: https://git.openjdk.java.net/jfx/pull/475