[AST] Allow Init accessors to be internal

Author: li3zhen1

lib/AST/AccessRequests.cpp

@@ -65,8 +65,8 @@ AccessLevelRequest::evaluate(Evaluator &evaluator, ValueDecl *D) const {
       // These are only needed to synthesize the setter.
       return AccessLevel::Private;
     case AccessorKind::Init:
-      // These are only called from designated initializers.
-      return AccessLevel::Private;
+      // These are only called from within the same module.
+      return std::min(storage->getFormalAccess(), AccessLevel::Internal);
     }
   }