Add symlink icon to file rows in repository browser

Summary

Before we refactored the Repository Browser to vue, we had a specific icon for symlinks (although no indication in the blob view):

Older fontawesome icons	New file type icons

In a separate issue, we should address the lack of a specific symlink icon and also add a label in the blob view: #215396 (closed)

Steps to reproduce

1. Open a folder with one symlink file in it. (example deployconfig.js in https://gitlab.com/redbaron1/diffbug/-/tree/master)
2. No specific symlink icon is shown.