RFR: 8091673: Public focus traversal API for use in custom controls [v6]

[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 incrementally with one additional commit since the last revision:

  visible

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1604/files
  - new: https://git.openjdk.org/jfx/pull/1604/files/3b834b48..59f92ab9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1604&range=05
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1604&range=04-05

  Stats: 10 lines in 2 files changed: 6 ins; 0 del; 4 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