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