code: def xml_path_completion(xml_path):
      
      if xml_path.startswith("/"):
          full_path = xml_path
      else:
          full_path = os.path.join(robosuite.models.assets_root, xml_path)
      return full_path
docs: Takes in a local xml path and returns a full path.
          if @xml_path is absolute, do nothing
          if @xml_path is not absolute, load xml that is shipped by the package