Recompilation speedup: Create AdminAPI.UserView to avoid compile-time dep

#2651 (closed)

This is basically the same thing as !3425 (merged), I just neglected a particular view when merging by mistake. This finishes the job and gets rid of a cycle: https://www.diffchecker.com/R5LhPQBZ

It makes MastodonAPI.AccountView a runtime dep instead of compile-time.