[ConstraintGraph] Make binding inference more incremental and stop resetting bindings

Author: xedin

include/swift/Sema/ConstraintGraph.h

@@ -124,6 +124,7 @@ class ConstraintGraphNode {
   void retractFromInference(Constraint *constraint, bool notifyFixedBindings);
   void reintroduceToInference(Constraint *constraint, bool notifyFixedBindings);
   void resetBindingSet();
+  void updateAdjacentVars() const;
   /// }
 
   /// The constraint graph this node belongs to.