RFR: 8227619: Potential memory leak in javafx.scene.control.ListView

[Ambarish Rapte]

`ListView` does not get GCed because `SelectedItemsReadOnlyObservableList` adds a `ListChangeListener` to the (`ObservableList`) items of `ListView`.

Adding a `WeakListChangeListener` instead of `ListChangeListener` fixes the issue.

Added a unit test and verified that existing tests do not fail due to this change.

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Commits:
 - 60ee7d03: 8227619: Potential memory leak in javafx.scene.control.ListView

Changes: https://git.openjdk.java.net/jfx/pull/84/files
 Webrev: https://webrevs.openjdk.java.net/jfx/84/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8227619
  Stats: 32 lines in 2 files changed: 28 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx/pull/84.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/84/head:pull/84

PR: https://git.openjdk.java.net/jfx/pull/84