EditEntity (entity select field) may discard selected values if the user is missing permissions on them

[sleidig]

To Reproduce
assume a user who has access only to children with a certain category.

1. Edit a Note that links to children, including some the current user cannot access
2. Trying to close the form causes a warning about unsaved changes - even without enabling edit mode
3. Editing and saving the note will discard the children from the entity-select field that this user cannot access

Expected behavior
We currently remove refs that are not found. Instead, we should probably keep them and display some placeholder chip in the select fields saying "not found or not accessible".