Fix the type forwarding of INotifyPropertyChanging

I'm not 100% sure this is the correct approach, but it fixes the `TypeLoadException` for `INotifyPropertyChanging` for me.

I had to change the namespace of `INotifyPropertyChanging` from `ReactiveUI` to `System.ComponentModel` I think type forwarding doesn't work if the type moves to a different namespace, please correct me if I'm wrong.

I'm also not 100% sure I've included all of the correct platforms, I can't test on a Mac or iOS