This fixes a few things:
- Previously, CreateSymbolicLink would always create a relative link if a `dir` was provided, but the relative-ness of a link should be determined by the target path, not the null-ness of the `dir`.
- Special handling is now done to symlink to 'rooted' paths correctly (they are treated as a relative link, which is different than how the xToPrefixedFileW functions treat them)
- ReadLink now correctly supports UNC paths via a new `ntToWin32Namespace` function which intends to be an analog of `RtlNtPathNameToDosPathName` (RtlNtPathNameToDosPathName is not used because it seems to heap allocate as it takes an RTL_UNICODE_STRING_BUFFER)