Lazy subscribe to collection changed.
Lazy subscribe to collection changed.

Subscribing to the inner collection's `CollectionChanged` event when an `ItemsSourceView` was created means the only way to unsubscribe is to dispose the `ItemsSourceView` meaning that the instance can't be easily shared.

wieslawsoltes/Perspex,jkoritzinsky/Perspex,Perspex/Perspex,wieslawsoltes/Perspex,AvaloniaUI/Avalonia,SuperJMN/Avalonia,wieslawsoltes/Perspex,SuperJMN/Avalonia,AvaloniaUI/Avalonia,AvaloniaUI/Avalonia,SuperJMN/Avalonia,AvaloniaUI/Avalonia,SuperJMN/Avalonia,SuperJMN/Avalonia,SuperJMN/Avalonia,AvaloniaUI/Avalonia,jkoritzinsky/Avalonia,jkoritzinsky/Avalonia,grokys/Perspex,jkoritzinsky/Avalonia,AvaloniaUI/Avalonia,AvaloniaUI/Avalonia,wieslawsoltes/Perspex,wieslawsoltes/Perspex,SuperJMN/Avalonia,jkoritzinsky/Avalonia,wieslawsoltes/Perspex,grokys/Perspex,jkoritzinsky/Avalonia,Perspex/Perspex,wieslawsoltes/Perspex,jkoritzinsky/Avalonia,jkoritzinsky/Avalonia