[jdk17u-dev] RFR: 8306955: Open source several JComboBox jtreg tests

[Victor Rudometov]

Clean backport, new tests, low risk
Checked on macOS x64, linux x64, windows x64, tests pass

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Commit messages:
 - Backport 1f689241cfcb4083cba283a2010b532948865283

Changes: https://git.openjdk.org/jdk17u-dev/pull/1363/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1363&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306955
  Stats: 392 lines in 5 files changed: 392 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1363.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1363/head:pull/1363

PR: https://git.openjdk.org/jdk17u-dev/pull/1363