RFR: 8346884: Add since checker test to jdk.editpad

[Nizar Benalla]

Please review this patch to add a new test to check `@since` tags in the `jdk.editpad` module.

TIA

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Commit messages:
 - add new `@since` test

Changes: https://git.openjdk.org/jdk/pull/25613/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25613&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346884
  Stats: 30 lines in 1 file changed: 30 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25613.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25613/head:pull/25613

PR: https://git.openjdk.org/jdk/pull/25613