Add an activatable widget to the action area of a `GtkInfoBar`.
This also connects a signal handler that will emit the [[email protected]:GtkInfoBar:response] signal on the message area
when the widget is activated. The widget is appended to the end of the message areas action area.
| this |
a `GtkInfoBar` |
| child |
an activatable widget |
| response_id |
response ID for |