Add additional SystemWeb HttpRequset properties to C# test stubs

Author: ewillonermsft

csharp/ql/test/resources/stubs/System.Web.cs

@@ -178,6 +178,37 @@ public class HttpRequest
         public string RawUrl { get; set; }
         public HttpCookieCollection Cookies => null;
         public bool IsAuthenticated { get; set; }
+        public NameValueCollection Form => null;
+        public NameValueCollection Headers => null;
+        public NameValueCollection Params => null;
+        public string UserAgent(string s) => null;
+        public string UrlReferrer(string s) => null;
+        public NameValueCollection ServerVariables => null;
+        // Default property that goes through the collections
+        //      QueryString, Form, Cookies, ClientCertificate and ServerVariables
+        public String this[String key]
+        {
+            get
+            {
+                String s;
+
+                s = QueryString[key];
+                if (s != null)
+                    return s;
+
+                s = Form[key];
+                if (s != null)
+                    return s;
+
+                HttpCookie c = Cookies[key];
+                if (c != null)
+                    return c.Value;
+
+                s = ServerVariables[key];
+                if (s != null)
+                    return s;
+            }
+        }
     }
 
     public class HttpRequestWrapper : System.Web.HttpRequestBase