RFR: 8268225: Support :focus-visible and :focus-within CSS pseudoclasses [v10]

[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 incrementally with one additional commit since the last revision:

  address review comments

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Changes:
  - all: https://git.openjdk.org/jfx/pull/475/files
  - new: https://git.openjdk.org/jfx/pull/475/files/0c7d6e72..40522b80

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=475&range=09
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=475&range=08-09

  Stats: 6 lines in 3 files changed: 2 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jfx/pull/475.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/475/head:pull/475

PR: https://git.openjdk.org/jfx/pull/475