Show unlock action for the file owner

[falkloewert]

Fixes #17837

Summary

The "Unlock file" entry was only shown when the current user owns the lock (lockOwnerId == userId). The server also allows the file owner to unlock TYPE_USER locks — OCA\FilesLock\Service\LockService::canUnlock():

if ($request->getType() === ILock::TYPE_USER && $isFileOwner) {
    return;
}

Without this, a stale lock created by another client (e.g. the Text app, lock owner text) cannot be released from the app at all; with the default lock_timeout = -1 it never expires.

Change: FileLockingHelper.canUserUnlockFile() now also accepts file.ownerId == userId.

Known limitation: for group folders and external storage the server deliberately skips the file-owner check (MountProvider allowlist in canUnlock), so the client cannot mirror the rule exactly there; the action can then fail with the existing error snackbar.

🖼️ Screenshots

Not applicable — the only visible difference is an additional entry in the file overflow menu.

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not needed — one added case; existing cases still pass (FileLockingHelperTest, 5 tests)
• 🔙 Backport requests are created or not needed: not needed
• 📅 Milestone is set
• 🌸 PR title is meaningful (if it should be in the changelog: is it meaningful to users?): "Unlock a file locked by another client"

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI — assistant-generated patch, reviewed and tested by me.