[jdk21u-dev] RFR: 8352905: Open some JComboBox bugs 1

[Satyen Subramaniam]

Backporting JDK-8352905: Open some JComboBox bugs 1. Adds four JComboBox tests. Ran GHA Sanity Checks and new tests directly. Patch is clean. Backporting for parity with Oracle.

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Commit messages:
 - Backport a55ccd267cdfbb7a52c0647fa3b2f93b36b1805f

Changes: https://git.openjdk.org/jdk21u-dev/pull/2445/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2445&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8352905
  Stats: 455 lines in 4 files changed: 455 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2445.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2445/head:pull/2445

PR: https://git.openjdk.org/jdk21u-dev/pull/2445