RFR: 8355522: Remove the `java.locale.useOldISOCodes` system property [v5]

[Naoto Sato]

> This PR removes the system property deprecated in JDK 25. If the property is specified at runtime, a warning will be emitted at startup to inform the user that the value is ignored. A corresponding CSR has been drafted as well

Naoto Sato has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - Reflects review comments
 - Merge branch 'master' into JDK-8355522-Remove-useOldISOCodes
 - Further wording refinement
 - Obsolete comment correction
 - Reflects review comments
 - initial commit

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26419/files
  - new: https://git.openjdk.org/jdk/pull/26419/files/c68a63be..965830aa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26419&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26419&range=03-04

  Stats: 664985 lines in 7465 files changed: 452015 ins; 138570 del; 74400 mod
  Patch: https://git.openjdk.org/jdk/pull/26419.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26419/head:pull/26419

PR: https://git.openjdk.org/jdk/pull/26419