Adds a execute and return result message (#383)

* inital request

* refactored query execution failure callback to take exception

* added failure callback to execute and return

* added test for query execute and return

* updated params

* removed dead code

* addressed feedback; added multiple active result set support; updated tests

* addessed feedback and added testing and errors and verification

* change <= to ==

* changed name of trashQ to removedQuery

src/Microsoft.SqlTools.ServiceLayer/QueryExecution/ResultOnlyContext.cs

@@ -0,0 +1,30 @@
+// 
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using Microsoft.SqlTools.Hosting.Protocol;
+using System.Threading.Tasks;
+using Microsoft.SqlTools.Hosting.Protocol.Contracts;
+
+namespace Microsoft.SqlTools.ServiceLayer.QueryExecution
+{
+    /// <summary>
+    /// Implementation of IEventSender that swallows events without doing anything with them.
+    /// In the future this class could be used to roll up all the events and send
+    /// them all at once
+    /// </summary>
+    public class ResultOnlyContext<TResult> : IEventSender
+    {
+        private readonly RequestContext<TResult> origContext;
+
+        public ResultOnlyContext(RequestContext<TResult> context) {
+            origContext = context;
+        }
+
+        public virtual async Task SendEvent<TParams>(EventType<TParams> eventType, TParams eventParams)
+        {
+            // no op to swallow events
+            // in the future this could be used to roll up events and send them back in the result
+        }
+    }
+}