[jdk21u-dev] RFR: 8311663: Additional refactoring of Locale tests to JUnit

[Goetz Lindenmaier]

I backport this for parity with 21.0.3-oracle.

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Commit messages:
 - Backport 71cac8ce47b69a2b78d54cbceb0f0510e5ea4cdc

Changes: https://git.openjdk.org/jdk21u-dev/pull/183/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=183&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311663
  Stats: 549 lines in 10 files changed: 159 ins; 217 del; 173 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/183.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/183/head:pull/183

PR: https://git.openjdk.org/jdk21u-dev/pull/183