Add CS::CSWindowImp class

[ThomasJClark]

Add partial definitions for the CSWindow base, which can be used to get the HWND instance for the game window and change various graphics quality preferences

e.g.:

auto window_ref = CS::CSWindowImp::instance();
if (window_ref.has_reference())
{
    auto &window = window_ref.reference();

    // Disable ray tracing
    window.get_graphics_settings().ray_tracing_quality = CS::CSWindowImp::quality_level::off;

    // Change the window title
    SetWindowTextA(window.get_window_handle(), "Bingus Bongus Ring");
}