RFR: 8330304: MenuBar: Invisible Menu works incorrectly with keyboard arrows [v2]

[Andy Goryachev]

> The root cause is that the skin used two fields to store one entity (`focusedMenu` and `focusedMenuIndex`), causing mismatch when invisible menu(s) are present.
> 
> The fix involves using a single index variable.
> 
> Also wanted to note that in theory, `openMenu` and `openMenuButton` can also be replaced with a single boolean, but I decided not to change these in order to keep the amount of diffs to a minimum.

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/1467/files
  - new: https://git.openjdk.org/jfx/pull/1467/files/cbe168e0..9443d1b2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1467&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1467&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 3 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1467.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1467/head:pull/1467

PR: https://git.openjdk.org/jfx/pull/1467