Centralize retained menu popup attachment

src/legacy_ui_overlay_services.h

@@ -6,6 +6,7 @@
 
 class App;
 class Node;
+class NodePopupMenu;
 
 namespace pp::panopainter {
 
@@ -15,6 +16,13 @@ void initialize_legacy_overlay_node(App& app, Node& node);
     App& app,
     const std::shared_ptr<Node>& node) noexcept;
 
+[[nodiscard]] pp::foundation::Result<std::shared_ptr<NodePopupMenu>> add_legacy_popup_menu(
+    App& app,
+    const char* template_id,
+    float x,
+    float y,
+    float rtl_anchor_width) noexcept;
+
 template <class T>
 std::shared_ptr<T> make_legacy_overlay_node(App& app)
 {