RFR: 8315898: Open source swing JMenu tests

[Abhishek Kumar]

Few closed JMenu swing tests are open sourced.

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Commit messages:
 - Open source swing JMenu tests

Changes: https://git.openjdk.org/jdk/pull/15639/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15639&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315898
  Stats: 357 lines in 6 files changed: 357 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15639.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15639/head:pull/15639

PR: https://git.openjdk.org/jdk/pull/15639