OUT / INOUT arguments in vfuncs not typed as pointers

[BlobCodes]

Example definition of Gtk::Widget._register_unsafe_do_measure

    private macro _register_unsafe_do_measure
      private def self._vfunc_unsafe_measure(%this : Pointer(Void), lib_orientation :  UInt32, lib_for_size :  Int32, lib_minimum :  Int32, lib_natural :  Int32, lib_minimum_baseline :  Int32, lib_natural_baseline :  Int32, ) : Void
# @orientation: 
# @for_size: 
# @minimum: (out) (transfer full) (optional) 
# @natural: (out) (transfer full) (optional) 
# @minimum_baseline: (out) (transfer full) (optional) 
# @natural_baseline: (out) (transfer full) (optional) 

        %gc_collected = !LibGObject.g_object_get_qdata(%this, GICrystal::GC_COLLECTED_QDATA_KEY).null?
        %instance = LibGObject.g_object_get_qdata(%this, GICrystal::INSTANCE_QDATA_KEY)
        raise GICrystal::ObjectCollectedError.new if %gc_collected || %instance.null?

        %instance.as(self).unsafe_do_measure(lib_orientation, lib_for_size, lib_minimum, lib_natural, lib_minimum_baseline, lib_natural_baseline)
      end

      def self._class_init(type_struct : Pointer(LibGObject::TypeClass), user_data : Pointer(Void)) : Nil
        vfunc_ptr = (type_struct.as(Pointer(Void)) + 232).as(Pointer(Pointer(Void)))
        vfunc_ptr.value = (->_vfunc_unsafe_measure(Pointer(Void), UInt32, Int32, Int32, Int32, Int32, Int32)).pointer
        previous_def
      end
    end

The last four arguments have to be pointers because their ArgInfo#direction are OUT. This is currently not accounted for.