RFR: 8310234: Refactor Locale tests to use JUnit [v2]

[Justin Lu]

> Please review this PR as apart of [JDK-8307843](https://bugs.openjdk.org/browse/JDK-8307843) which refactors some tests in Locale to use JUnit. Other cleanup and small changes are included as well. More refactoring in Locale tests will be done in separate PRs.
> 
> If the test had a bugNNNNN.java name, it was also renamed to something more [descriptive](https://openjdk.org/jtreg/faq.html#how-should-i-name-a-test).
> 
> Below is a list of all the changes,
> 
> - Refactor Bug4316602.java as LocaleConstructors.java
> - Refactor Bug4210525.java as CaseCheckVariant.java
> - Refactor bug6277243.java as RootLocale.java
> - Refactor bug6312358.java as GetInstanceCheck.java
> - Refactor Bug8154797.java as CompareProviderFormats.java
> - Refactor Bug8004240.java as GetAdapterPreference.java
> - Refactor bug4122700.java into AvailableLocalesTest.java (and combined with StreamAvailableLocales.java)

Justin Lu has updated the pull request incrementally with one additional commit since the last revision:

  Review: Clarify LocaleConstructors.java with comment for each test method

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14609/files
  - new: https://git.openjdk.org/jdk/pull/14609/files/02252fb5..63256db3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14609&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14609&range=00-01

  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14609.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14609/head:pull/14609

PR: https://git.openjdk.org/jdk/pull/14609