LegacyJoystickDriver implements the legacy IJoystickDriver interface
(GameWindow.Joysticks) in terms of the new IJoystickDriver2 interface
(OpenTK.Input.Joystick).
This removes a large chunk of code from each platform backend, as they
no longer need to implement IJoystickDriver themselves. Additionally,
it adds support for device hot plugging which was previously missing.
