Images are deleted if a URI is reused

Problem/Motivation

Drupal's UI makes sure that the URI is unique by appending suffixes in the media library, this is not guaranteed on the Rokka metadata entities or file entities.

At least for Rokka metadata entities we can add this constraint to make sure that the relationship is unidirectionally unique, see #3197548: Metadata URI is not guaranteed to be unique (only one metadata entity is ever returned for a URI).

That leaves the case that for some reason multiple file entities reference the same Rokka metadata entity. In this case deletion of the file will check if there rae other URI with the same hash to make sure not to delete those but it does not check for multiple files.

Proposed resolution

Add this check.