RFR: 8299423: JavaFX Mac system menubar leaks [v5]

[Michael Strauß]

On Fri, 13 Jan 2023 09:18:56 GMT, Florian Kirmaier <fkirmaier at openjdk.org> wrote:

>> This PR fixes the leak in the mac system menu bar.
>> 
>> Inside the native code, NewGlobalRef is called for the callable.
>> Which makes it into a "GC-Root" until DeleteGlobalRef is called.
>> 
>> The DeleteGlobalRef is never called for the MenuEntry, if it's removed from the menu without removing it's callable.
>> This PR adds logic, whether the Menu is inserted. If it's not inserted in a Menu anymore, then DeleteGlobalRef is called, by calling `_setCallback` with the callable "null".
>> 
>> The unit test verifies, that this bug happened without this change, but no longer happens with this change.
>
> Florian Kirmaier has updated the pull request incrementally with one additional commit since the last revision:
> 
>   JDK-8299423
>   we now use the junit5 api

Marked as reviewed by mstrauss (Committer).

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PR: https://git.openjdk.org/jfx/pull/987