Implement Widget::overlay for Responsive widget

lazy/src/cache.rs

@@ -0,0 +1,13 @@
+use iced_native::overlay;
+use iced_native::Element;
+
+use ouroboros::self_referencing;
+
+#[self_referencing(pub_extras)]
+pub struct Cache<'a, Message: 'a, Renderer: 'a> {
+    pub element: Element<'a, Message, Renderer>,
+
+    #[borrows(mut element)]
+    #[covariant]
+    pub overlay: Option<overlay::Element<'this, Message, Renderer>>,
+}