<i18n dev> RFR: 8357882: Use UTF-8 encoded data in LocaleDataTest

[Naoto Sato]

Test refactoring stemmed from the discussion at https://git.openjdk.org/jdk/pull/25228#discussion_r2106755160. The test is now based on UTF-8 instead of ISO-8859-1

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Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/25524/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25524&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357882
  Stats: 4205 lines in 2 files changed: 0 ins; 101 del; 4104 mod
  Patch: https://git.openjdk.org/jdk/pull/25524.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25524/head:pull/25524

PR: https://git.openjdk.org/jdk/pull/25524