RFR: 8318204: Use new EventTarget methods in ListenerHelper

Tue Oct 17 04:52:46 UTC 2023

As of OpenJFX 21, `EventTarget` has methods to add and remove event listeners.
The `instanceof` checks in `com.sun.javafx.scene.control.ListenerHelper` should be removed and replaced by a simple call to the respective interface method.

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Commit messages:
 - Use new EventTarget methods in ListenerHelper

Changes: https://git.openjdk.org/jfx/pull/1262/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1262&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318204
  Stats: 87 lines in 2 files changed: 1 ins; 78 del; 8 mod
  Patch: https://git.openjdk.org/jfx/pull/1262.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1262/head:pull/1262

PR: https://git.openjdk.org/jfx/pull/1262