mount method
Inserts this element into the tree under parent and builds it.
Implementation
@override
void mount(Element? parent, BuildOwner owner) {
this.parent = parent;
this.owner = owner;
mounted = true;
_state.attach(widget as StatefulWidget, buildContext, _markNeedsBuild);
_registerGlobalKey();
_state.initState();
_state.didChangeDependencies();
performRebuild();
}