Test the presence of a given layer type.

        :param class_: Layer class you're interested in.
        :param became: Allow transformed layers in results

def has_layer(self, class_: Type[L], became: bool=True) -> bool:
        """
        Test the presence of a given layer type.

        :param class_: Layer class you're interested in.
        :param became: Allow transformed layers in results
        """

        return (class_ in self._index or
                (became and class_ in self._transformed))