Rename Widget::on_event to update

widget/src/themer.rs

@@ -110,7 +110,7 @@ where
             .operate(tree, layout, renderer, operation);
     }
 
-    fn on_event(
+    fn update(
         &mut self,
         tree: &mut Tree,
         event: Event,
@@ -121,7 +121,7 @@ where
         shell: &mut Shell<'_, Message>,
         viewport: &Rectangle,
     ) {
-        self.content.as_widget_mut().on_event(
+        self.content.as_widget_mut().update(
             tree, event, layout, cursor, renderer, clipboard, shell, viewport,
         );
     }