<i18n dev> RFR: 8308108: Support Unicode extension for collation settings

[Naoto Sato]

This change intends to interpret the BCP47 U extension wrt collation settings in the given `Locale`, then applies them to the created instances in the 1-arg factory method in `Collator`. A corresponding CSR has also been drafted.

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Commit messages:
 - 8308108: Support Unicode extension for collation settings

Changes: https://git.openjdk.org/jdk/pull/14040/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14040&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308108
  Stats: 113 lines in 2 files changed: 112 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14040.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14040/head:pull/14040

PR: https://git.openjdk.org/jdk/pull/14040