Generalize instantiations with interface

[yav]

Cryptol allows "passing through" parameters like this:

module F where
  import interface I
  submodule M = G { interface I }

This means that when F is instantiated with some module A, M will be defined by instantiating G with the same M.

At present, I needs to always be a parameter to the current functor. It would make sense to generalize this to allow I be a parameter of an outer functor too, for example, like this:

module OuterF where
  import interface I
  submodule Inner where
    submodule M = G { interface I }

Note that in this case Inner is not a functor and has not parameters, but the definition of M still makes sense.

This should be fairly easy to implement, because at present the instantiation G { interface I } is implemented by desugaring to an anonymous module:

submodule M = G { interface I }
--->
submodule Anon where
   x = I::x
   ...

submodule M = G { Anon }

This exact same thing should work if I was a parameter to an outer functor too, so mostly we'd have to modify the code to look for the closest enclosing matching parameter.