[jdk17u-dev] RFR: 8310234: Refactor Locale tests to use JUnit

[Goetz Lindenmaier]

I backport this for parity with 17.0.15-oracle.

Omitted StreamAvailableLocales.java. It came with enhancement "8282319: java.util.Locale method to stream available Locales" in 21.

The remaining edits all are caused by "8283698: Refactor Locale constructors used in src/test" which is not in 17.

Deleted test/jdk/java/util/Locale/Bug4316602.java by hand.

Resolved test/jdk/java/util/Locale/CaseCheckVariant.java, CompareProviderFormats.java and RootLocale.java.

Removed test cases with Locale.of() from LocaleConstructors.java

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Commit messages:
 - Backport dad7bd9efc7ca2c245f7e35267479670f93a53a8

Changes: https://git.openjdk.org/jdk17u-dev/pull/3242/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=3242&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310234
  Stats: 899 lines in 13 files changed: 474 ins; 425 del; 0 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/3242.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/3242/head:pull/3242

PR: https://git.openjdk.org/jdk17u-dev/pull/3242