RFR: 8300409: Create an automated regression test for JComboBox titled border issues(JDK-8300269)

[Manukumar V S]

Create a automated regression test for JComboBox titled border issues([JDK-8300269](https://bugs.openjdk.org/browse/JDK-8300269)).

This test passes in JDK-20-ea+16 and fails in JDK-20-ea+16 and above.

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Commit messages:
 - 8300409: Create an automated regression test for JComboBox titled border issues(JDK-8300269)

Changes: https://git.openjdk.org/jdk/pull/12061/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12061&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300409
  Stats: 176 lines in 1 file changed: 176 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12061.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12061/head:pull/12061

PR: https://git.openjdk.org/jdk/pull/12061