Handle the ActionDefineFunction action.

def _handle_actiondefinefunction(self, _):
        """Handle the ActionDefineFunction action."""
        obj = _make_object("ActionDefineFunction")
        obj.FunctionName = self._get_struct_string()
        obj.NumParams = unpack_ui16(self._src)
        for i in range(1, obj.NumParams + 1):
            setattr(obj, "param" + str(i), self._get_struct_string())
        obj.CodeSize = unpack_ui16(self._src)
        yield obj