MenuItem
Description:
[ CCode ( has_construct_function = false ) ]
public MenuItem (string? label, string? detailed_action)
  public MenuItem (string? label, string? detailed_action)
Creates a new MenuItem.
If label is non-null it is used to set the "label" attribute of the new item.
If detailed_action is non-null it is used to set the "action" and possibly the "target" 
      attribute of the new item. See set_detailed_action for more 
      information.
Parameters:
| label | 
           the section label, or null  | 
      
| detailed_action | 
           the detailed action string, or null  | 
      
Returns:
| 
           a new MenuItem  |