c290a38730
Since commit ed3b8d093e16, the actor's single-child policy is enforced even when using the generic add/remove_child() methods. This makes it possible to follow GTK/AdwBin's lead and replace out custom child allocation with a BinLayout, without changing the actor's semantics in a fundamental way. However this does change slightly how the child is allocated, as it now only expands according to its expand properties, not when the alignment is set to FILL. Even after the preparations in the previous commit, some fallout is still likely, but it will be easy to address, and the cleanup is significant enough to justify it. Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3046>