macos: Retrieve NSEvents based on event properties

We cannot depend on the exact event, since some events (e.g. for popups)
are rewritten. Therefore we need to determine the NSEvent based on
heuristics. The usual suspects are event type, device and timestamp.

This allows us to fix IMContext for popups.

gdk/macos/gdkmacosdisplay.c

@@ -998,7 +998,9 @@ _gdk_macos_display_get_nsevent (GdkEvent *event)
     {
       const GdkToNSEventMap *map = iter->data;
 
-      if (map->gdk_event == event)
+      if (map->gdk_event->event_type == event->event_type &&
+          map->gdk_event->device == event->device &&
+          map->gdk_event->time == event->time)
         return map->nsevent;
     }