File Provider: support symbolic link operations

[bpasero]

With the new file service we can support move/copy across file system providers for files and folders. However, if one of the items is a symbolic link, there is currently no way to re-create such a link on the target provider.

In node.js terms there is a method called symlink.

I think conceptually we would need new API such as link(source, target) and then providers have to deal with the quirks.

On top of that we also need a way to resolve the target of the link, otherwise we cannot make a decision how to restore it.

Bottom line: I think it only makes sense to preserve symlinks if they are self contained in the data that is being moved/copied, not when pointing outside.

[irvnriir]

Always should be a way to copy/preserve all symlinks .