Test to check that when doing a deep substitution inside a signature,
that items that reference that element are still correctly resolved
even if they're in a different path.

  $ cat m.mli
  module type S = sig
    module M: sig
      type t
    end
    type t = M.t
  end
  module type T = S with type M.t := int
  

In this, we want to check that the type `t` in module type `T` has
its RHS correctly replaced with an `int`

  $ ocamlc -c -bin-annot m.mli
  $ odoc compile m.cmti
  $ odoc link m.odoc
  $ odoc html-generate m.odocl --indent -o .
  $ odoc_print m.odocl -r T.t
  {
    "id": {
      "`Type": [
        { "`ModuleType": [ { "`Root": [ "None", "M" ] }, "T" ] },
        "t"
      ]
    },
    "doc": [],
    "equation": {
      "params": [],
      "private_": "false",
      "manifest": {
        "Some": {
          "Constr": [
            { "`Resolved": { "`Identifier": { "`CoreType": "int" } } },
            []
          ]
        }
      },
      "constraints": []
    },
    "representation": "None"
  }
 
