[1/2] shlwapi/tests: Add wvnsprintfW comformance test

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://testbot.winehq.org/JobDetails.pl?Key=22849

Your paranoid android.


=== wxppro (32 bit string) ===
string: unhandled exception c0000005 at 77F6923B

=== w2003std (32 bit string) ===
string: unhandled exception c0000005 at 7D18A782