RFR: 8310234: Refactor Locale tests to use JUnit [v3]

[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 four additional commits since the last revision:

 - Method signature is too long
 - Exceptions in GetInstanceCheck.java are distinct, catch clause should be reserved for the underlying exception
 - Rename method to be more clear in CaseCheckVariant.java
 - Method name case in AvailableLocalesTest.java

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14609/files
  - new: https://git.openjdk.org/jdk/pull/14609/files/63256db3..c84b3ea0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14609&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14609&range=01-02

  Stats: 10 lines in 3 files changed: 4 ins; 0 del; 6 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