RFR: 8268225: Support :focus-visible and :focus-within CSS pseudoclasses [v4]

[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.

Michael Strauß has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 16 additional commits since the last revision:

 - Merge branch 'master' of https://github.com/mstr2/jfx into feature/focusvisible
 - changes per discussion, added test
 - wording
 - Re-ordered methods
 - 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
 - ... and 6 more: https://git.openjdk.java.net/jfx/compare/8c12b454...50ec08f6

-------------

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/475/files
  - new: https://git.openjdk.java.net/jfx/pull/475/files/9d79df63..50ec08f6

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=475&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=475&range=02-03

  Stats: 341137 lines in 6581 files changed: 184453 ins; 110765 del; 45919 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