Container listings from filesystem do not include symlinks

[RubenVerborgh]

When starting a server from the filesystem, symlinks are accessible as (dereferenced) resources through GET, but they do not show up in a container listing.

For example, if I start the server on a folder with contents

• bar
• foo symlinked to bar

then both /bar and /foo will work, but / will only list bar.

This is likely due to https://github.com/solid/community-server/blob/93b71eb72688cc501a9435325699eea55b93974c/src/storage/accessors/FileDataAccessor.ts#L279 only accepting files or folders. However, getData will gladly accept them.

I think the behavior should at least be consistent: either we expose them and list them, or we do not expose them.
My preference is exposing them.