Make it possible to use our row widgets in a GtkListView
HdyPreferencesRow and its subclasses are all
GtkListBoxRow subclasses. That's nice for
GtkListBox, but it also means that it breaks in a
GtkListView where we can't control the row widget.
This leads to the following hierarchy of css nodes:
which of course breaks the styles. Moreover, it means that the style for isolated expanded rows that we use is fundamentally impossible.