Handle tags with the same name gracefully

[kesselb]

Summary

We received a report that some files marked as favorites are not displayed in the "Favorites" view. Additionally, users cannot remove the favorite state from these files. This issue is similar to #49395.

Root Cause

• The lib/private/Tags.php implementation does not properly verify if a given tag already exists. Although a check exists, the list of tags is loaded only once and never updated.
• The database table lacks a unique constraint, allowing multiple identical tags for the same user.

Proposed Solution

To avoid requiring a migration path for existing tags, I adjusted the code to handle tags with the same name gracefully.

Commit: "vobjects may contain the same tag with different ids"

• Resolves the display issue by using a subselect to find all tag IDs associated with a name and fetching the relevant objects.

Commit: "add mapper for vcategory_to_object"

• Introduces a TagRelation and TagRelationMapper to clean up the codebase and address the deletion issue.
• This makes it possible to delete mappings for multiple categorieid values, which previously only targeted the first ID.

Current Status

The implementation requires additional work to fully resolve the deletion issue. However, due to higher-priority tickets, we are unable to allocate further time to this effort at the moment.

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)