RFR: 8294589: MenuBarSkin: memory leak when changing skin [v14]

[Andy Goryachev]

> Fixed memory leak by using weak listeners and making sure to undo everything that has been done to MenuBar/Skin in dispose().
> 
> This PR depends on a new internal class ListenerHelper, a replacement for LambdaMultiplePropertyChangeListenerHandler.
> See https://github.com/openjdk/jfx/pull/908

Andy Goryachev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 46 commits:

 - Merge remote-tracking branch 'origin/master' into
   8294589.menubarskin.leak
 - 8294589: testing github merge-conflict label behavior
 - 8294589: cleanup
 - Merge remote-tracking branch 'origin/master' into
   8294589.menubarskin.leak
 - Merge branch '8294809.listener.helper' into 8294589.menubarskin.leak
 - 8294809: generics
 - 8294589: owner
 - Merge branch '8294809.listener.helper' into 8294589.menubarskin.leak
 - 8294809: is alive
 - Merge branch '8294809.listener.helper' into 8294589.menubarskin.leak
 - ... and 36 more: https://git.openjdk.org/jfx/compare/0a785ae0...45f3e374

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Changes: https://git.openjdk.org/jfx/pull/906/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=906&range=13
  Stats: 465 lines in 2 files changed: 235 ins; 198 del; 32 mod
  Patch: https://git.openjdk.org/jfx/pull/906.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/906/head:pull/906

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