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/IRequestSender.cs

@@ -0,0 +1,27 @@
+//
+// 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.Hosting.Contracts;
+
+namespace Microsoft.SqlTools.Hosting.Protocol
+{
+    /// <summary>
+    /// Interface for objects that can requests via the JSON RPC channel
+    /// </summary>
+    public interface IRequestSender
+    {
+        /// <summary>
+        /// Sends a request over the JSON RPC channel. It will wait for a response to the message
+        /// before completing.
+        /// </summary>
+        /// <param name="requestType">Configuration of the request to send</param>
+        /// <param name="requestParams">Parameters for the request to send</param>
+        /// <typeparam name="TParams">Type of the parameters for the request, defined by <paramref name="requestType"/></typeparam>
+        /// <typeparam name="TResult"></typeparam>
+        /// <returns></returns>
+        Task<TResult> SendRequest<TParams, TResult>(RequestType<TParams, TResult> requestType, TParams requestParams);
+    }
+}