dinput: Implement DIPROP_KEYNAME property for keyboard device

[Sergey Khodych]

> 
>> ...
>> +                hr = SysKeyboardWImpl_GetObjectInfo( (LPDIRECTINPUTDEVICE8W)iface , &didoi,
>> +                                                     ps->diph.dwObj, ps->diph.dwHow );
> 
> You mixing unicode and ascii. Also if you are implementing 
> SysKeyboardAImpl_GetProperty you should also implement it's unicode 
> counterpart SysKeyboardWImpl_GetProperty.
Realization of GetProperty for keyboard device for unicode and ascii do
not differ at this time.