Mangling: add a few utility functions in the new mangler and demangler which will be used by reflection mangling

include/swift/Basic/Demangler.h

@@ -114,6 +114,8 @@ public:
 
   NodePointer demangleTopLevel();
 
+  NodePointer demangleType();
+
 private:
 
   void addSubstitution(NodePointer Nd) {
@@ -166,6 +168,8 @@ private:
     return createWithChild(kind, popNode(Node::Kind::Type));
   }
 
+  void parseAndPushNodes();
+
   NodePointer changeKind(NodePointer Node, Node::Kind NewKind);
 
   NodePointer demangleOperator();