Improved handling of calls inside values for inlining reports

[poechsel]

Take the following code sample:

(* File Foo.ml *)
module A = struct
  let a = f ()
end

Inlining reports were showing the call to f to happen in Foo while it actually happened under Foo.A.
The reason behind this misreporting was that the scoping information wasn't used when creating
the relative path for a call.
This PR use the location information on the call to build the correct relative path. This is fine
because closure conversion won't inline Lambda terms directly: the inliner is only able to inline
terms that were only visited and does not even try to maintain correct debuginfo -- or histories --
on those.