Adds an activatable widget to the action area of a `GtkDialog`.
GTK connects a signal handler that will emit the [[email protected]:GtkDialog:response] signal on the dialog when the widget
is activated. The widget is appended to the end of the dialog’s action area.
If you want to add a non-activatable widget, simply pack it into the action_area field of the `GtkDialog` struct.
| this |
a `GtkDialog` |
| child |
an activatable widget |
| response_id |
response ID for |