Move the subscription to LocationChanged and Deactivated Window events to OnLoaded.

[KristinaKoeva]

When you have one single WPF Window and its Content is a WebView, you could simulate reloading of the WebView, by disposing the old one and creating a new one. This causes the
OnVisualParentChanged to execute two times, for the old and new WebView. The Window is the same so the following code,
window->LocationChanged += _handler; window->Deactivated += _handler;
executes two times. When the location of the Window changes the handler for the old, disposed view is invoked, which is incorrect and causes exceptions.

[KristinaKoeva]

Hey,

Unfortunately there are still few cases when Window::GetWindow(oldParent) returns null. The last commit stores the window reference, so that we could use it to unsubscribe from the events.