RFR: 8318613: ChoiceFormat patterns are not well tested

[Justin Lu]

Please review this PR which adds a test for ChoiceFormat intended to test a wide range of ChoiceFormat patterns.

The existing test _Bug4387255_ only tests a singular basic pattern and does not test for incorrect patterns either.

The new test checks 

- both correct and incorrect patterns
- the behavior of incorrect patterns that either throw an IllegalArgumentException or discard the incorrect portion
- the case of formatting with an empty pattern (that leads to empty limits and formats)

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Commit messages:
 - add test for AIOOBE
 - cleanup
 - init

Changes: https://git.openjdk.org/jdk/pull/16324/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16324&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318613
  Stats: 142 lines in 1 file changed: 142 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16324.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16324/head:pull/16324

PR: https://git.openjdk.org/jdk/pull/16324