RFR: 8268225: Support :focus-visible and :focus-within CSS pseudoclasses [v8]

[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 21 additional commits since the last revision:

 - Update copyright headers
 - Merge branch 'master' into feature/focusvisible
 - fixed undeterministic test failures
 - minor wording change
 - restart github actions
 - Merge branch 'master' of https://github.com/mstr2/jfx into feature/focusvisible
 - changes per discussion, added test
 - wording
 - Re-ordered methods
 - remove code comment
 - ... and 11 more: https://git.openjdk.java.net/jfx/compare/129c1ffa...bd57bbac

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

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/475/files
  - new: https://git.openjdk.java.net/jfx/pull/475/files/d9a715e3..bd57bbac

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=475&range=07
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=475&range=06-07

  Stats: 473015 lines in 7841 files changed: 268935 ins; 144862 del; 59218 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