We currently assume that any '::destroy' signal on a GObject type
has the semantics of the ClutterActor/GtkWidget signal, and should
therefore result in all signals being disconnected.
But we already have a case where the assumption doesn't hold: ShellWM
uses '::destroy' for the closing animation of windows, and the ShellWM
object itself remains very valid after the emission.
So rather than making assumptions about '::destroy', check objects
against a list of destroyable types that are explicitly registered
as such.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2226>
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