RFR: JDK-8317631: Refactor ChoiceFormat tests to use JUnit [v2]

[Justin Lu]

> Please review this PR which refactors the ChoiceFormat tests to use JUnit.

Justin Lu has updated the pull request incrementally with one additional commit since the last revision:

  Review: separate into two tests

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16065/files
  - new: https://git.openjdk.org/jdk/pull/16065/files/bd10afa8..fcd8ebfa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16065&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16065&range=00-01

  Stats: 40 lines in 1 file changed: 18 ins; 0 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/16065.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16065/head:pull/16065

PR: https://git.openjdk.org/jdk/pull/16065