RFR: 8353585: Provide ChoiceFormat#parse(String, ParsePosition) tests

[Justin Lu]

Please review this PR which provides unit tests for `ChoiceFormat#parse(String, ParsePosition)` to check default, multi match, and no match behavior. There were no existing relevant tests.

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

Commit messages:
 - more cases + cleanup
 - init

Changes: https://git.openjdk.org/jdk/pull/24395/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24395&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8353585
  Stats: 74 lines in 1 file changed: 74 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/24395.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24395/head:pull/24395

PR: https://git.openjdk.org/jdk/pull/24395