Instead of fetching user infos separately, we can fetch them with the rest of the infos.

Depends on D9656

Generate some updates, reintroduce old code, and compare new with old result using _.isEqual.
For one update, generated during sending a friend request to an unknown user, the contents don't match. That seems to expose a race condition which was already present in our code (we're fetching the users a little earlier now) - going to investigate it further.