RFR: 8310683: Refactor StandardCharset/standard.java to use JUnit [v2]

[Justin Lu]

> Please review this PR which is apart of the migration of JDK tests to JUnit. Standard.java is refactored to use JUnit, and thus split up into the following tests.
> 
> - typeTest
> - nameMethodTest
> - forNameMethodTest
> - charsetModifiersTest
> - correctCharsetsTest
> 
>  Additionally all unused methods were removed.

Justin Lu has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14621/files
  - new: https://git.openjdk.org/jdk/pull/14621/files/e7277ca0..e7277ca0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14621&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14621&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14621.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14621/head:pull/14621

PR: https://git.openjdk.org/jdk/pull/14621