insertRenderObjectChild abstract method
Insert the given child into renderObject at the given slot.
The semantics of
slot are determined by this element. For example, if
this element has a single child, the slot should always be null. If this
element has a list of children, the previous sibling element wrapped in an
IndexedSlot is a convenient value for the slot.
@protected void insertRenderObjectChild(covariant RenderObject child, covariant Object? slot);