notifications: BEL and OSC-777 now focuses the window on notification activation

Or put more propertly; if the notification daemon, and the
notification helper used by foot has been configured
properly (i.e. they both support XDG activation tokens), notifications
generated by BEL and OSC-777 will now raise/focus the window when the
default action of the notification is activated - typically by
clicking the notification.

Closes #1822

osc.c

@@ -558,9 +558,10 @@ osc_notify(struct terminal *term, char *string)
     }
 
     notify_notify(term, &(struct notification){
-        .title = (char *)title,
-        .body = (char *)msg,
+        .title = xstrdup(title),
+        .body = xstrdup(msg),
         .expire_time = -1,
+        .focus = true,
     });
 }