RFR: 8294589: MenuBarSkin: memory leak when changing skin

[Andy Goryachev]

On Thu, 29 Sep 2022 23:00:17 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

> Fixed memory leak by using weak listeners and making sure to undo everything that has been done to MenuBar/Skin in dispose().

I have a string feeling that this PR should go back to DRAFT state, pending a better listener helper implementation JDK-8294809.  Also, this particular skin may need to get it's listeners refactored - I see two scene listeners which seems redundant.

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PR: https://git.openjdk.org/jfx/pull/906