Invoked to inform the page that it is attached to the current request. This occurs when a page is first referenced within a request. If the page was created from scratch for this request, the call to {@link #loaded()} will preceded the call to {@link #attached()}.
First all listeners have {@link PageLifecycleListener#restoreStateBeforePageAttach()} invoked, followed by{@link PageLifecycleListener#containingPageDidAttach()}.