RFR: 8343739: Test java/awt/event/KeyEvent/ExtendedKeyCode/ExtendedKeyCodeTest.java failed: Wrong extended key code

[Alisen Chung]

Test was failing on Ubuntu, looks to be a synchronous error in the test so I rewrote it to improve stability.

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Commit messages:
 - update test and improve stability

Changes: https://git.openjdk.org/jdk/pull/24885/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24885&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343739
  Stats: 75 lines in 1 file changed: 40 ins; 26 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/24885.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24885/head:pull/24885

PR: https://git.openjdk.org/jdk/pull/24885