Add support for keyboard scancode

[xobs]

The keydown and keyup handlers provide translated characters. For example, if I press the b key, then I get an event with KeyEventArgs.Key == 'b', and KeyEventArgs.NativeKeyCode == 45.

However, if I switch my keyboard to Dvorak and press the exact same key, I get KeyEventArgs.Key == 'x' and KeyEventArgs.NativeKeyCode == 67.

It is understandable that the Key changes, because the layout has changed. However, the NativeKeyCode should remain the same. Failing that, an additional property with the scancode should be added.