RFR: 8091673: Public focus traversal API for use in custom controls [v9]

[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 15 additional commits since the last revision:

 - newline
 - Merge remote-tracking branch 'origin/master' into 8091673.focus.traversal.2
 - the
 - review comments
 - visible
 - review comments
 - Merge remote-tracking branch 'origin/master' into 8091673.focus.traversal.2
 - review comments
 - review comments
 - request focus traversal
 - ... and 5 more: https://git.openjdk.org/jfx/compare/c5e528b7...b82c37d4

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1604/files
  - new: https://git.openjdk.org/jfx/pull/1604/files/3ea6778b..b82c37d4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1604&range=08
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1604&range=07-08

  Stats: 1292 lines in 32 files changed: 127 ins; 534 del; 631 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