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

terminal.c

@@ -3597,9 +3597,10 @@ term_bell(struct terminal *term)
 
     if (term->conf->bell.notify) {
         notify_notify(term, &(struct notification){
-            .title = (char *)"Bell",
-            .body = (char *)"Bell in terminal",
+            .title = xstrdup("Bell"),
+            .body = xstrdup("Bell in terminal"),
             .expire_time = -1,
+            .focus = true,
         });
     }