fix issue 11232 - rewritten std.windows.syserror.sysErrorString

Fixed for Unicode-correctness; now works on non-English Windows systems.
Added unit test.
Throws an Exception if the given error code or language combination
was invalid.
Merge pull request #1634 from JakobOvrum/syserrorstring

fix issue 11232 - rewritten std.windows.syserror.sysErrorString