RFR: 8295506: ButtonBarSkin: memory leak when changing skin

[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

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Commit messages:
 - Merge remote-tracking branch 'origin/master' into
 - 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"
 - 8295506: button bar skin
 - 8294809: removed weak listeners support
 - 8294809: use weak reference correctly this time
 - 8294809: tests
 - ... and 12 more: https://git.openjdk.org/jfx/compare/3376228a...6a61be7d

Changes: https://git.openjdk.org/jfx/pull/921/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=921&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295506
  Stats: 25 lines in 2 files changed: 17 ins; 3 del; 5 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