runWidget method
Implementation
void runWidget(Widget widget) {
FocusManager.instance.dispose();
FocusManager.instance.setTestKeyEvents(keyboard.keyEvents);
FocusManager.instance.initialize();
_rootElement = widget.createElement();
_rootElement!.mount(null);
_build(_rootElement!);
_layout(_rootElement!);
outputBuffer.smartClear();
paintElement(_rootElement!);
}