[jdk21u-dev] RFR: 8310818: Refactor more Locale tests to use JUnit

[Goetz Lindenmaier]

I backport this for parity with 21.0.4-oracle.

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Commit messages:
 - Backport 12e943091071b02b5756b57527a5f86a3d881cb8

Changes: https://git.openjdk.org/jdk21u-dev/pull/360/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=360&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310818
  Stats: 1377 lines in 13 files changed: 681 ins; 686 del; 10 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/360.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/360/head:pull/360

PR: https://git.openjdk.org/jdk21u-dev/pull/360