Rename Widget::on_event to update

widget/src/container.rs

@@ -297,7 +297,7 @@ where
         );
     }
 
-    fn on_event(
+    fn update(
         &mut self,
         tree: &mut Tree,
         event: Event,
@@ -308,7 +308,7 @@ where
         shell: &mut Shell<'_, Message>,
         viewport: &Rectangle,
     ) {
-        self.content.as_widget_mut().on_event(
+        self.content.as_widget_mut().update(
             tree,
             event,
             layout.children().next().unwrap(),