Function widget 

pub fn widget(child: impl IntoUiNode, id: impl IntoValue<WidgetId>) -> UiNode

Create a widget node that wraps child and introduces a new widget context. The node defines an WIDGET context and implements the widget in each specific node method.

This node must wrap the outer-most context node in the build, it is the WidgetBase widget type.

The node retains the widget state if build with cfg(any(test, feature = "test_util"))), otherwise the state is cleared.