VE requirement (Epic: T245299):

• As someone editing a sub-reference in VE, you should not be able to accidentally "orphan" sub-references by deleting their parent reference

User Story:
As an editor editing an article in VE
I want to see that a parent reference has subreferences when editing the parent in a popup
So that I can avoid changing or deleting a parent reference without also changing or deleting its subreferences

Proposed implementation:
Show a remark in the popup, “this parent has N sub references" (tbc)