RFR: 8091673: Public focus traversal API for use in custom controls [v5]

[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

Andy Goryachev 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 10 additional commits since the last revision:

 - review comments
 - Merge remote-tracking branch 'origin/master' into 8091673.focus.traversal.2
 - review comments
 - review comments
 - request focus traversal
 - 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:
  - all: https://git.openjdk.org/jfx/pull/1604/files
  - new: https://git.openjdk.org/jfx/pull/1604/files/c8b7b2ed..3b834b48

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1604&range=04
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1604&range=03-04

  Stats: 2219 lines in 52 files changed: 253 ins; 1948 del; 18 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