Fix missing Visitors

Author: darrelmiller

src/Microsoft.OpenApi/Services/OpenApiVisitorBase.cs

@@ -276,6 +276,20 @@ public virtual void Visit(OpenApiSecurityRequirement securityRequirement)
         {
         }
 
+        /// <summary>
+        /// Visits <see cref="OpenApiSecurityScheme"/>
+        /// </summary>
+        public virtual void Visit(OpenApiSecurityScheme securityScheme)
+        {
+        }
+
+        /// <summary>
+        /// Visits <see cref="OpenApiExample"/>
+        /// </summary>
+        public virtual void Visit(OpenApiExample example)
+        {
+        }
+
         /// <summary>
         /// Visits list of <see cref="OpenApiTag"/>
         /// </summary>
@@ -325,5 +339,13 @@ public virtual void Visit(IDictionary<string, OpenApiServerVariable> serverVaria
         public virtual void Visit(IDictionary<string, OpenApiEncoding> encodings)
         {
         }
+
+        /// <summary>
+        /// Visits IOpenApiReferenceable instances that are references and not in components
+        /// </summary>
+        /// <param name="referenceable">referenced object</param>
+        public virtual void Visit(IOpenApiReferenceable referenceable)
+        {
+        }
     }
 }

src/Microsoft.OpenApi/Services/OpenApiWalker.cs

@@ -995,6 +995,14 @@ internal void Walk(OpenApiSecurityScheme securityScheme)
             Walk(securityScheme as IOpenApiExtensible);
         }
 
+        /// <summary>
+        /// Visits <see cref="OpenApiSecurityScheme"/> and child objects
+        /// </summary>
+        internal void Walk(IOpenApiReferenceable referenceable)
+        {
+            _visitor.Visit(referenceable);
+        }
+
         /// <summary>
         /// Dispatcher method that enables using a single method to walk the model
         /// starting from any <see cref="IOpenApiElement"/>
@@ -1057,7 +1065,12 @@ private void Walk(string context, Action walk)
         /// </summary>
         private bool IsReference(IOpenApiReferenceable referenceable)
         {
-            return referenceable.Reference != null && !_inComponents;
+            var isReference = referenceable.Reference != null && !_inComponents;
+            if (isReference)
+            {
+                Walk(referenceable);
+            }
+            return isReference;
         }
 
         private void EnterComponents()