Reference in "summary" field to a relation widget shows value_field, not display field

[madsem]

When referencing a relationship widget inside a summary field, the wrong value is displayed.

Expected it to display the value of display_fields and not as it currently is, the value_field.
Because the value_field holds the indentifier, which most often not what the user should see.

Example:

Reference:
#3616 (comment)