If the InternalItemNode holding a main ref's footnote body is never deleted and remains in the InternalList indexes, then it can be used to to avoid orphaning and serialize to a main+details ref tag. This will become the new source of truth which replaces synthetic list-defined main refs.
Currently, ve.dm.MWReferenceNode#removeFromInternalList will remove the InternalItemNode corresponding to a ref from the index when that ref is deleted. This breaks some sub-referencing use cases, for example when a main ref is deleted but its sub-reference remains. Always leave the index pointing a an InternalItemNode intact.
Acceptance Criteria
- Deleted but sub-referenced main ref still serializes as a main+details (status quo)
- Footnote numbering remains sequential (status quo)
- Both main and sub-ref footnote body can still be edited (status quo)
- "pure" main ref is still visible in the reuse dialog and can be reused into a standalone main ref.
- Unused refs (including no subrefs) are not shown in the references list.