The `notes.json` endpoint doesn't return sufficient information to
build a functional discussion for a diff note, so we don't bother
at the moment, instead pulling anew from `discussions.json`. However,
this is quite expensive, and we're hoping to replace `discussions.json`
with `notes.json` entirely in the future, so we're going to need it to
support these attributes.

Including information about the diff makes `notes.json` a little more
expensive, but it's a paginatable endpoint with incremental updates,
whereas `discussions.json` is not paginatable and always returns all
notes for a given noteable, so this seems like an uncontroversial win.