code: def _LayoutShapeFactory(shape_elm, parent):
      
      tag_name = shape_elm.tag
      if tag_name == qn('p:sp') and shape_elm.has_ph_elm:
          return LayoutPlaceholder(shape_elm, parent)
      return BaseShapeFactory(shape_elm, parent)
docs: Return an instance of the appropriate shape proxy class for *shape_elm*
      on a slide layout.