RFR: 8316285: Opensource JButton manual tests

[Abhishek Kumar]

Few closed JButton swing manual test converted to automated and open sourced.

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Commit messages:
 - Opensource JButton manual tests

Changes: https://git.openjdk.org/jdk/pull/15835/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15835&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316285
  Stats: 297 lines in 3 files changed: 297 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15835.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15835/head:pull/15835

PR: https://git.openjdk.org/jdk/pull/15835