`LocalFileSystem.isdir` inconsistent with `os.path.isdir` with symbolic links

[ethanwharris]

We had a bit of a subtle bug here: Lightning-AI/pytorch-lightning#6730

Because LocalFileSystem.info returns t: 'link' for sym linked files / directories, isdir will always be false. This is inconsistent with the behaviour of os.path.isdir which follows sym links. We've been able to fix this by overriding isdir to just return os.path.isdir. I guess that this behaviour isn't intended? Not sure what the best fix is, overriding isdir works but is not the prettiest solution 😃

[martindurant]

I think it would be fair to follow whatever os does. It will mean breaking the weak requirement that info["type"] be "directory", but I'm not too worried about that.