[SHLWAPI] Add test for PathUnExpandEnvStringsForUser

In 2k3, IShellLinkW::SetIconLocation calls shlwapi private PathUnExpandEnvStringsForUserW function internally. See GetIconLocation.txt. This text file is the analysis result by using ShellLinkTest.zip and "API Monitor".

This patch path-unexpand.patch will add the testcase of PathUnExpandEnvStringsForUserW. This testcase was successfully tested.