replace method
Implementation
replace(Route newRoute, Element newElement, Route? oldRoute) {
_Page newPage = _Page(newRoute, newElement);
_Page? oldPage;
if (oldRoute != null) {
oldPage = _findPage(oldRoute);
_removeAllAfter(oldPage);
}
_stack.add(newPage);
_task.addReplace(newPage, oldPage);
}