This allows text appearing on a specific GDS layer:purpose pair
to be interpreted as a port. This does not quite match the
intended behavior of such layers, since it is implied that any
layer geometry coincident with the text should form the area of
the port, which is not (yet) handled. Also, it is presumably
implied that the port order matches the order in which text
appears in the GDS stream, but magic does not preserve this
order when re-writing any GDS output.