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  |