user32: Implement GetWindowModuleFileName with tests

[Dmitry Timoshkov]

"Dmitry Timoshkov" <dmitry at codeweavers.com> wrote:

>> +    hproc = OpenProcess(PROCESS_QUERY_INFORMATION, 0, pid);
> 
> After reading MSDN and guessing from the API name shouldn't it
> simply fetch GWL_HINSTANCE and call GetModuleFileName on it?

And after looking at GetModuleFileNameW implementation, shouldn't it
treat hModule == 0 as GetModuleHandle(0) and not be 16-bit specific?
Guess this all needs a test case.

-- 
Dmitry.