Take mount name into account when searching by filename.

[icewind1991]

• Resolves: #

Summary

Currently, searching only takes the filename as it exists in the filecache into account. This doesn't (always) work for the root of mounts though.

Renamed shares and the root of groupfolder/external storages aren't matched because their name in the filesystem isn't the same as the name for their cache entry.

This solves that by also taking the name of the mountpoint into account when searching

• Add regex_substring to the query builder
• Add mount_path_name as a field in the filecache search, which gets transformed to a substring of mount_path
• Transform a dav search on filename to searching on both filename and mount_path_name

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