fix(files): preserve destination path for dropped directories

[Zhey-on]

• Resolves: [Bug]: DropService subdirectory 404 #58760

Summary

Dropping a folder into a subdirectory was creating missing directories with a path that did not include the destination folder.

In practice, that sent WebDAV requests to the wrong location and produced PROPFIND 404 / PUT 404 for nested folder uploads.

This change keeps directory creation anchored to destination.path, so folder drops into subdirectories stay in the selected target.

I also added a regression test that verifies nested directories are created under the destination path.

TODO

• Add regression test coverage for nested directory drops into a subdirectory target
• Run post-fix manual checks in the browser (drag/drop into root and into nested subdirectories, then confirm no DAV 404 in logs)

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[susnux]

I am pretty sure this is already fixed with #58680