[scn] mv definition of SCN to dir of share

src/sql/engine/expr/ob_expr.h

@@ -459,6 +459,8 @@ public:
     return OBJ_DATUM_STRING == obj_datum_map_;
   };
 
+  inline bool is_const_expr() const { return is_static_const_ || is_dynamic_const_; }
+
   // Evaluate all parameters, assign the first sizeof...(args) parameters to %args.
   //
   // e.g.: