GenericSpecializer: fix a bug which prevented specialization for typealiases in some cases

Need to canonicalize the replacement type. Otherwise it could be generic if it is a typealias inside a generic type, e.g.
```
  struct S<T> {
    typealias I = Int
  }
```

Author: eeckstein

lib/SILOptimizer/Utils/Generics.cpp

@@ -601,7 +601,7 @@ bool ReabstractionInfo::prepareAndCheck(ApplySite Apply, SILFunction *Callee,
 
     // Check only the substitutions for the generic parameters.
     // Ignore any dependent types, etc.
-    auto Replacement = Type(GP).subst(CalleeParamSubMap);
+    auto Replacement = Type(GP).subst(CalleeParamSubMap)->getCanonicalType();
     if (!Replacement->is<ArchetypeType>())
       HasNonArchetypeGenericParams = true;