[jdk25u] RFR: 8371094: --mac-signing-key-user-name no longer works

[Alexey Semenyuk]

Almost clean backport of https://github.com/openjdk/jdk/pull/28120 PR with trivial conflict resolution.

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Commit messages:
 - 8371094: --mac-signing-key-user-name no longer works

Changes: https://git.openjdk.org/jdk25u/pull/366/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u&pr=366&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371094
  Stats: 13 lines in 3 files changed: 11 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk25u/pull/366.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u.git pull/366/head:pull/366

PR: https://git.openjdk.org/jdk25u/pull/366