Add a new placeholder shape based on *placeholder*.

def clone_placeholder(self, placeholder):
        """
        Add a new placeholder shape based on *placeholder*.
        """
        sp = placeholder.element
        ph_type, orient, sz, idx = (
            sp.ph_type, sp.ph_orient, sp.ph_sz, sp.ph_idx
        )
        id_ = self._next_shape_id
        name = self._next_ph_name(ph_type, id_, orient)
        self._spTree.add_placeholder(id_, name, ph_type, orient, sz, idx)