feat: dnd destination for stack widget

widget/src/stack.rs

@@ -375,6 +375,28 @@ where
         }
     }
 
+    fn drag_destinations(
+        &self,
+        state: &Tree,
+        layout: Layout<'_>,
+        renderer: &Renderer,
+        dnd_rectangles: &mut crate::core::clipboard::DndDestinationRectangles,
+    ) {
+        for ((e, c_layout), state) in self
+            .children
+            .iter()
+            .zip(layout.children())
+            .zip(state.children.iter())
+        {
+            e.as_widget().drag_destinations(
+                state,
+                c_layout.with_virtual_offset(layout.virtual_offset()),
+                renderer,
+                dnd_rectangles,
+            );
+        }
+    }
+
     fn overlay<'b>(
         &'b mut self,
         tree: &'b mut Tree,