<i18n dev> RFR: JDK-8318189: ChoiceFormat::format throws undocumented AIOOBE

[Justin Lu]

Please review this PR which makes an `ArrayIndexOutOfBoundsException` apparent in ChoiceFormat::format.

An _incomplete_ ChoiceFormat can be created, which is not revealed until format is invoked.

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Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/16587/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16587&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318189
  Stats: 13 lines in 1 file changed: 11 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16587.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16587/head:pull/16587

PR: https://git.openjdk.org/jdk/pull/16587