Rename Widget::on_event to update

widget/src/stack.rs

@@ -204,7 +204,7 @@ where
         });
     }
 
-    fn on_event(
+    fn update(
         &mut self,
         tree: &mut Tree,
         event: Event,
@@ -224,7 +224,7 @@ where
             .zip(tree.children.iter_mut().rev())
             .zip(layout.children().rev())
         {
-            child.as_widget_mut().on_event(
+            child.as_widget_mut().update(
                 state,
                 event.clone(),
                 layout,