shell32[2/2]: implements shell link's GetCurFile (with tests, fixes bug #21297) [try4]

[Mikołaj Zalewski]

Juan Lang pisze:
> Hi Mikolaj, this one was rejected due to formatting, I imagine because
> of C++ comments in the tests:
>
> +    // Setting the same value will not set IsDirty...
>
> Would you mind fixing and resending?  Thanks,
> --Juan
>   
  Yes, I've sent the old patch with C++ comments (and a typo). I should
be able to generate a correct one today.

Mikołaj