RFR: 8357281: sun.util.Locale.LanguageTag should be immutable

[Justin Lu]

_sun.util.Locale.LanguageTag_ is essentially a BCP47 language tag data carrier for Locale. The class, once created is not modified; the class should be made immutable. Converting the class to a record accomplishes this and also simplifies some of the existing code.

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Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/25371/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25371&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357281
  Stats: 180 lines in 3 files changed: 15 ins; 69 del; 96 mod
  Patch: https://git.openjdk.org/jdk/pull/25371.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25371/head:pull/25371

PR: https://git.openjdk.org/jdk/pull/25371