RFR: 8315761: Open source few swing JList and JMenuBar tests

[Abhishek Kumar]

Few closed JList and JMenubar swing tests are open sourced.

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Commit messages:
 - Open source few swing JList and JMenubar tests

Changes: https://git.openjdk.org/jdk/pull/15621/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15621&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315761
  Stats: 250 lines in 4 files changed: 250 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15621.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15621/head:pull/15621

PR: https://git.openjdk.org/jdk/pull/15621