RFR: 8366568: Allow replacing built in application menu in system menu bar

[Martin Fox]

This PR provides an API for replacing the application menu that JavaFX places in the system menu bar on macOS. The application menu is the one next to the Apple menu that is titled with the application's name and contains the Quit menu item. The JavaFX version of this menu has many limitations so this PR allows a developer to simply replace it outright.

Technically there’s no reason to restrict this to only one menu so the API allows the developer to specify an observable list of Menus known as the common system menus. Like the current application menu the common menus are present for all JavaFX windows and remain present even if all windows lose focus. Any per-window menus provided by a MenuBar with useSystemMenuBar set will appear alongside the common system menus.

In addition the PR provides some calls that allow a developer to implement the Hide <app name>, Hide Others, and Show All menu items that are expected in the application menu.

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Commit messages:
 - Merge remote-tracking branch 'upstream/master' into commonmenus
 - Specify a list of menus that are always present in the system menu bar

Changes: https://git.openjdk.org/jfx/pull/1881/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1881&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366568
  Stats: 586 lines in 12 files changed: 560 ins; 21 del; 5 mod
  Patch: https://git.openjdk.org/jfx/pull/1881.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1881/head:pull/1881

PR: https://git.openjdk.org/jfx/pull/1881