RFR: 8295506: ButtonBarSkin: memory leak when changing skin [v3]

[Andy Goryachev]

> as determined by SkinMemoryLeakTest (remove line 165) and a leak tester
> https://github.com/andy-goryachev-oracle/Test/blob/main/src/goryachev/apps/LeakTest.java
> 
> Make sure to configure the current test in LeakTest:
> protected final Type WE_ARE_TESTING = Type.BUTTON_BAR;
> 
> 
> caused by:
> - adding and not removing listeners
> - adding and not removing children Nodes

Andy Goryachev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 25 commits:

 - 8295506: cleanup
 - Merge remote-tracking branch 'origin/master' into 8295506.button.bar.skin
 - Merge remote-tracking branch 'origin/master' into
   8295506.button.bar.skin
 - Merge remote-tracking branch 'origin/master' into
   8295506.button.bar.skin
 - Merge branch '8294809.listener.helper' into 8295506.button.bar.skin
 - 8294809: generics
 - Merge branch '8294809.listener.helper' into 8295506.button.bar.skin
 - 8294809: is alive
 - Revert "8294809: removed weak listeners support"
   
   This reverts commit 2df4a85db638d76cacaf6c54ba669cdb3dd91a18.
 - 8295506: button bar skin
 - ... and 15 more: https://git.openjdk.org/jfx/compare/4a19fe71...efc60c0c

-------------

Changes: https://git.openjdk.org/jfx/pull/921/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=921&range=02
  Stats: 30 lines in 2 files changed: 17 ins; 9 del; 4 mod
  Patch: https://git.openjdk.org/jfx/pull/921.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/921/head:pull/921

PR: https://git.openjdk.org/jfx/pull/921