signalTracker: Explicitly register destroyable types

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>

js/ui/environment.js

@@ -345,6 +345,8 @@ function init() {
         SignalTracker.addObjectSignalMethods(prototype);
     };
 
+    SignalTracker.registerDestroyableType(Clutter.Actor);
+
     // Miscellaneous monkeypatching
     _patchContainerClass(St.BoxLayout);