Push an item onto the state's stack of locations.

def push_location(
            self,
            element_path,  # type: Text
            array_index=None  # type: Optional[int]
    ):
        # type: (...) -> None
        """Push an item onto the state's stack of locations."""
        location = ProcessorLocation(element_path=element_path, array_index=array_index)
        self._locations.append(location)