RFR: 8091673: Public focus traversal API for use in custom controls [v3]

[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 is a lightweight change that only adds the public API for focus traversal, containing neither the public API for the traversal policy (#1555) nor with the changes for the traversal policy hidden (#1604).

Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:

  review comments

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1628/files
  - new: https://git.openjdk.org/jfx/pull/1628/files/8be95cb4..3d034276

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1628&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1628&range=01-02

  Stats: 182 lines in 2 files changed: 180 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1628.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1628/head:pull/1628

PR: https://git.openjdk.org/jfx/pull/1628