Promise.with_change_func
Description:
[ CCode ( has_construct_function = false ) ]
public Promise.with_change_func (owned PromiseChangeFunc func)
  public Promise.with_change_func (owned PromiseChangeFunc func)
func will be called exactly once when transitioning out of gst_promise_result_pending into any 
      of the other PromiseResult states.
Parameters:
| func | a PromiseChangeFunc to call | 
| notify | notification function that  | 
| user_data | argument to call  | 
Returns:
| a new Promise |