Create MS.SqlTools.Credentials project (#249)

* Initial credential service files

* Clean-up hostloader

* Update build scripts to build credentials archive

* Move hosting files to new assembly

* Add credentials files to MS.SqlTools.Credentials

* Remove duplicate files

* Update namespace in program.cs

* Fix test build breaks

* Update extensions visibility.

* Remove unused resource strings

* Add xproj files to SLN for appveyor builds

* Fix appveyor build break in test project

* Fix extensibility tests

* Fix various typos in latest iteration

* Add settings for Integration build

* Fix codecoverage.bat to use full pdb for new projects

* Fix bug when packing in folder with native images

* Fix typos in xproj

* Reset XLF to fix build.cmd

src/Microsoft.SqlTools.Hosting/Hosting/Protocol/RequestContext.cs

@@ -0,0 +1,50 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System.Threading.Tasks;
+using Microsoft.SqlTools.ServiceLayer.Hosting.Protocol.Contracts;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.SqlTools.ServiceLayer.Hosting.Protocol
+{
+    public class RequestContext<TResult> : IEventSender
+    {
+        private readonly Message requestMessage;
+        private readonly MessageWriter messageWriter;
+
+        public RequestContext(Message requestMessage, MessageWriter messageWriter)
+        {
+            this.requestMessage = requestMessage;
+            this.messageWriter = messageWriter;
+        }
+
+        public RequestContext() { }
+
+        public virtual async Task SendResult(TResult resultDetails)
+        {
+            await this.messageWriter.WriteResponse(
+                resultDetails,
+                requestMessage.Method,
+                requestMessage.Id);
+        }
+
+        public virtual async Task SendEvent<TParams>(EventType<TParams> eventType, TParams eventParams)
+        {
+            await this.messageWriter.WriteEvent(
+                eventType,
+                eventParams);
+        }
+
+        public virtual async Task SendError(object errorDetails)
+        {
+            await this.messageWriter.WriteMessage(
+                Message.ResponseError(
+                    requestMessage.Id,
+                    requestMessage.Method,
+                    JToken.FromObject(errorDetails)));
+        }
+    }
+}
+