Turn the arguments of functors into COFEs + write some docs

See merge request iris/iris!257

This allows one to make use of recursive ghost state obtained from the
recursive domain equation solver.

Resolution of prophecy variables can be attached to atomic expressions

See merge request iris/iris!244

Arrays

See merge request iris/iris!245

Make functors a `Record` instead of a `Structure`.

See merge request iris/iris!256

We never make canonical instances of them.

Relax subG mode

See merge request iris/iris!255

More simple changes to make proof mode terms more compact.

See merge request iris/iris!253

With Coq master, we otherwise fail to infer instances with subG_savedAnythingΣ, which leads to goals like

> looking for (subG
>                       (@savedAnythingΣ (@ofe_funCF val (fun _ : val => laterCF idCF))
>                          ?cFunctorContractive0) Σ)

This is a follow up of !248.