Move unused forked code to external directory (#1192)

* Move unused forked code to external directory

* Fix SLN build errors

* Add back resource provider core since it's referenced by main resource provider project

* Update PackageProjects step of pipeline

external/Microsoft.SqlTools.Hosting.v2/Protocol/IJsonRpcHost.cs

@@ -0,0 +1,28 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+namespace Microsoft.SqlTools.Hosting.Protocol
+{
+    /// <summary>
+    /// Interface for a JSON RPC host
+    /// </summary>
+    public interface IJsonRpcHost : IEventSender, IRequestSender, IMessageDispatcher
+    {
+        /// <summary>
+        /// Starts the JSON RPC host 
+        /// </summary>
+        void Start();
+        
+        /// <summary>
+        /// Stops the JSON RPC host
+        /// </summary>
+        void Stop();
+        
+        /// <summary>
+        /// Waits for the JSON RPC host to exit
+        /// </summary>
+        void WaitForExit();
+    }
+}