RFR: 8353322: Specification of ChoiceFormat#parse(String, ParsePosition) is inadequate

[Justin Lu]

Please review this PR which specifies the `ChoiceFormat#parse(String, ParsePosition)` method. A corresponding CSR is filed. The current specification is simply "Parses a Number from the input text" which does not indicate how the value is returned. The criteria for a match, as well as no match should be made clear.

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Commit messages:
 - call 2-arg parse in example
 - init

Changes: https://git.openjdk.org/jdk/pull/24361/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24361&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8353322
  Stats: 20 lines in 1 file changed: 17 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/24361.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24361/head:pull/24361

PR: https://git.openjdk.org/jdk/pull/24361