Single file diff views

Created by: dadlerj

Related to #13410 (closed)

Requested by:

• https://app.hubspot.com/contacts/2762526/company/1686989427
• https://app.hubspot.com/contacts/2762526/company/2428850551

Both customers are interested in seeing arbitrary diffs (which we already provide), but for a single file at a time (which we do not). We don't have any way to fetch this from the backend or to display it today.