Comment thread in file commit view

A commit view currently has a comment thread.
A file view currently does not have any comment thread.
Proposal: Take the comment thread of a commit view, and expose it all file commit views for that commit.
- For example, this commit view has a comment thread: https://gitlab.com/victorwu/gitlab-metrics/commit/9599407f4a6b82896ba0c30121349574ee8ebe9c.
- That commit view has five files. In each of those files, at that commit, put in the same exact comment thread.
- It is the same comment thread, exposed in five different places. If there's a new comment in one of them, it is updated in the other.