gh-129333: fix import error over nfs on Windows by ChrisDenton · Pull Request #129616 · python/cpython

On Windows, realpath uses `GetFinalPathNameByHandleW` to resolve paths. This returns paths starting with a `\\?\` prefix, which is usually not what we want.

This change attempts to remove the prefix for \\?\UNC\ paths. A similar thing was already done for drive paths such as \\?\C:\.