get_activation_token
Description:
Gets the activation token of the notification.
If an an action is currently being activated, return the activation token. This function is intended to be used in a [callback@ActionCallback] to get the activation token for the activated action, if the notification daemon supports it.
Parameters:
| this | 
           The notification.  | 
      
Returns:
| 
           The current activation token, or null if none  |