RFR: 8090456: Focus Management

[Andy Goryachev]

Public APIs for focus traversal and the focus traversal policy:

https://github.com/andy-goryachev-oracle/Test/blob/main/doc/FocusTraversal/FocusTraversal.md

This work is loosely based on the patch
https://cr.openjdk.org/~jgiles/8061673/

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

Commit messages:
 - Merge remote-tracking branch 'origin/master' into 8090456.focus.traversal
 - whitespace
 - 8090456: focus traversal

Changes: https://git.openjdk.org/jfx/pull/1555/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1555&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8090456
  Stats: 3618 lines in 57 files changed: 1581 ins; 1543 del; 494 mod
  Patch: https://git.openjdk.org/jfx/pull/1555.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1555/head:pull/1555

PR: https://git.openjdk.org/jfx/pull/1555