<i18n dev> RFR: 8310234: Refactor Locale tests to use JUnit

[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)

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Commit messages:
 - Minor cleanup to various files
 - Refactor Bug8004240.java as GetAdapterPreference.java
 - Revert "Rename bug4123285.java as LocalesInApplet.java + minor cleanup, do not refactor to junit as depends on Applet"
 - Typo in CompareProviderFormats.java
 - Refactor Bug8154797.java as CompareProviderFormats.java
 - Rename bug4123285.java as LocalesInApplet.java + minor cleanup, do not refactor to junit as depends on Applet
 - Refactor bug6312358.java as GetInstanceCheck.java
 - Refactor bug6277243.java as RootLocale.java
 - Case of vars in LocaleConstructors.java
 - Refactor Bug4210525 as CaseCheckVariant
 - ... and 4 more: https://git.openjdk.org/jdk/compare/3e0bbd29...02252fb5

Changes: https://git.openjdk.org/jdk/pull/14609/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14609&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310234
  Stats: 1104 lines in 15 files changed: 597 ins; 507 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