[Windows] Add wmain code snippet

[longnguyen2004]

Since we have a main code snippet, can we have a wmain code snippet as well? It's mainly for completeness, and also using wmain is the only way to get Unicode from argv on Windows

[sean-mcmanus]

Fix is in https://github.com/microsoft/vscode-cpptools/releases/tag/0.30.0-insiders5 .