Centralize retained message dialog close callbacks

src/legacy_ui_overlay_services.h

@@ -82,4 +82,11 @@ void bind_legacy_click_destroys_node(ButtonT& button, Node& target) noexcept
     };
 }
 
+inline std::function<void(Node*)> legacy_destroy_node_callback(Node& target)
+{
+    return [&target](Node*) {
+        target.destroy();
+    };
+}
+
 } // namespace pp::panopainter