[Quartz] Set the popup menu type hint before realizing the popup.

Otherwise when operating a combo in fullscreen mode the GdkWindow for the popup is created using GDK_WINDOW_TYPE_HINT_NORMAL and in Quartz that's passed on to the GdkQuartzNSWindow with the result that in Fullscreen the combo opens as a separate full-screen window instead of as an appropriately sized window positioned over the combo.