RFR: 8091673: Public focus traversal API for use in custom controls

[Andy Goryachev]

Public focus traversal API for use in custom controls

https://github.com/andy-goryachev-oracle/Test/blob/main/doc/FocusTraversal/FocusTraversal-v3.md

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

And is a scaled down version (with the public traversal policy API removed) of
#1555

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Commit messages:
 - node focus traversal
 - internal traversal direction
 - Merge remote-tracking branch 'origin/master' into 8091673.focus.traversal.2
 - doc
 - 8091673: Public focus traversal API for use in custom controls

Changes: https://git.openjdk.org/jfx/pull/1604/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1604&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8091673
  Stats: 3749 lines in 55 files changed: 1479 ins; 1580 del; 690 mod
  Patch: https://git.openjdk.org/jfx/pull/1604.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1604/head:pull/1604

PR: https://git.openjdk.org/jfx/pull/1604