object-manager: look into the proxy object when checking constraints on a global

This allows having constraints on the pw properties and the GObject
properties of the proxy, instead of just on the global properties.

This is only useful for constraints on impl proxies, since the globals
coming from the registry don't have a proxy object associated at the
time they are added in the object managers

lib/wp/object-manager.c

@@ -447,7 +447,8 @@ wp_object_manager_is_interested_in_global (WpObjectManager * self,
   pw_array_for_each (i, &self->interests) {
     if (g_type_is_a (global->type, i->g_type)
         && (!i->constraints ||
-            check_constraints (i->constraints, global->properties, NULL)))
+            check_constraints (i->constraints, global->properties,
+                G_OBJECT (global->proxy))))
     {
       *wanted_features = i->wanted_features;
       return TRUE;