No way to set accessible relations in GtkListItem(Widget) or GtkColumnView{Row,Cell}(Widget)

In nautilus, we've been walking up the widget hierarchy to reach the private widgets GtkListItemWidget / GtkColumnViewRowWidget to call gtk_accessible_update_relation() on them, specifically for GTK_ACCESSIBLE_RELATION_LABELLED_BY. If that was not ugly enough, this is done in the first emission of ::bind (it cannot be done in ::setup because there is no parent yet).

For GtkListItemWidget maybe this relationship could be set implicitly by GTK, acting as a proxy for the application-privided child.

But for GtkColumnViewRowWidget GTK doesn't know which of the cells is the one labelling the row (in nautilus, that's the cell in the filename column). So, maybe GtkColumnViewRow should implement the GtkAccessible interface (as a proxy for the private GtkColumnViewRowWidget)?