[UX] move contents of "Manage file display" page

This is a follow-up to https://github.com/backdrop/backdrop-issues/issues/2632

The goal is to get rid of the "Manage file display" page entirely. We should move the settings that are currently on that page under a "configure" link on the File row on the usual "manage displays" page. A good example of what this would look like can be found on any other fieldable entity.

Example of configure link (closed):

Example of configure link (open):

Current settings on the "Manage file display" page:

Destination for these settings:

---

Advocate: @jenlampton

---

Weekly update?

---

PR: ?