Apply functor instantiation map to types

If a functor contains both a newtype and a type synonym referring to the
newtype, then during instantiation we must apply the instantiation map
to the types in the functor, so that the type synonym now refers to the
instantiated newtype instead. Previously, we only applied type
substitutions to the types in the functor, which would replace type
variables with concrete types defined in the functor arguments, but
would not replace any actual names. (Confusingly, the code refers to the
instantiation map as "value substitutions" even though it can contain
names in the type namespace. The "type substitutions" and "value
substitutions" are better thought of as "TVar -> Type mappings" and
"Name -> Name mappings".)

Fixes #1590.

src/Cryptol/TypeCheck/ModuleInstance.hs

@@ -82,7 +82,7 @@ instance ModuleInstance (ModuleG name) where
            }
 
 instance ModuleInstance Type where
-  moduleInstance = doTInst
+  moduleInstance = doTVInst
 
 instance ModuleInstance Schema where
   moduleInstance = doTInst