<i18n dev> RFR: 8342582: user.region for formatting number no longer works for 21.0.5

[Naoto Sato]

This is a regression caused by the fix to [JDK-8321206](https://bugs.openjdk.org/browse/JDK-8321206), where the default locale with `user.region` creation is inadvertently broken. Fix is to restore the user.region override within StaticProperty initialization.

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Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/21645/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21645&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342582
  Stats: 101 lines in 3 files changed: 74 ins; 20 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/21645.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21645/head:pull/21645

PR: https://git.openjdk.org/jdk/pull/21645