@id: the ID of an engine as reported by script_engine_list.
Function to be provided by the module to create an instance of one of the engines implemented by the module.
Return value: a newly created #PangoEngine of the specified type, or %NULL if an error occurred. (In normal operation, a module should not return %NULL. A %NULL return is only acceptable in the case where system misconfiguration or bugs in the driver routine are encountered.)