RFR: 8359108: Mac - When Swing starts First, native application menu doesn't work for JavaFX

[Pabulaner IV]

This pull request fixes the system menu bar on Mac when combining windows of Swing and JavaFX.

The first issue was to get the native menu bar working simultaneously on Swing and JavaFX, which was done by just returning always true inside the supportsSystemMenu method.

The second issue was to remove all system menu items installed by a swing window. This was fixed by checking the system menu bar every time an item is inserted or removed and removing all menu items that are not owned by JavaFX. This check is done on every insert and remove as JavaFX does not have a clear method inside the MenuBarDelegate class that could be called every time the window gets the focus.

I tested the fix with two Swing and two JavaFX windows that are run inside the same application and it works without any errors.

Co-Author: @FlorianKirmaier

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Commit messages:
 - 8359108: Mac - When Swing starts First, native application menu doesn't work for JavaFX

Changes: https://git.openjdk.org/jfx/pull/1835/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1835&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8359108
  Stats: 42 lines in 4 files changed: 27 ins; 12 del; 3 mod
  Patch: https://git.openjdk.org/jfx/pull/1835.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1835/head:pull/1835

PR: https://git.openjdk.org/jfx/pull/1835