RFR: 8338882: Clarify matching order of MessageFormat subformat factory styles

[Justin Lu]

Please review this PR which clarifies that the matching order of format styles for MessageFormat sub formats is not guaranteed by the JDK implementation. A corresponding CSR has also been drafted.

This is relevant when a locale provides equivalent patterns for multiple format factory styles. For example, a locale X could provide some equivalent date style "xyz" for both a MEDIUM and LONG style. Thus invoking toPattern() could output `date`, `date,medium`, or `date,long` depending on the order of such matching.

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Commit messages:
 - minor wording change
 - init

Changes: https://git.openjdk.org/jdk/pull/20695/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20695&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338882
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20695.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20695/head:pull/20695

PR: https://git.openjdk.org/jdk/pull/20695