[jdk21u-dev] RFR: 8310234: Refactor Locale tests to use JUnit

[Goetz Lindenmaier]

I backport this for parity with 21.0.4-oracle.

-------------

Commit messages:
 - Backport dad7bd9efc7ca2c245f7e35267479670f93a53a8

Changes: https://git.openjdk.org/jdk21u-dev/pull/358/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=358&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310234
  Stats: 1112 lines in 15 files changed: 605 ins; 507 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/358.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/358/head:pull/358

PR: https://git.openjdk.org/jdk21u-dev/pull/358