RFR: 8356107: [java.lang] Use @requires tag instead of exiting based on os.name or separatorChar property

[Brent Christian]

For `java.lang` tests, use the `@requires` facility in place of checking the `os.name` system property or `File.separatorChar`.

Automated test results are omitted as expected.

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Commit messages:
 - add @requires

Changes: https://git.openjdk.org/jdk/pull/25163/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25163&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356107
  Stats: 20 lines in 4 files changed: 4 ins; 10 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/25163.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25163/head:pull/25163

PR: https://git.openjdk.org/jdk/pull/25163