MockFileSystem's IDirectoryInfo.Create implementation fails with \\?\C:\Foo style paths

[mostynb]

Describe the bug

I need to use \\?\C:\Foo style paths on windows, in order to support long paths.

var longPath = @"\\?\C:\some\really\long\string\would\be\here.txt";
var fileSystem = new MockFileSystem();
var parent = fileSystem.Directory.GetParent(longPath);
parent.Create(); // This throws an exception because of the `?` character in the path.

If I use a regular FileSystem instead of MockFileSystem in the code above, there is no exception thrown.

[github-actions]

This is addressed in release v22.0.15.