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/IServiceHost.cs

@@ -0,0 +1,31 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System;
+using System.Threading.Tasks;
+using Microsoft.SqlTools.DataProtocol.Contracts;
+using Microsoft.SqlTools.Hosting.Protocol;
+
+namespace Microsoft.SqlTools.Hosting
+{
+    /// <summary>
+    /// Interface for service hosts. Inherits interface requirements for JSON RPC hosts
+    /// </summary>
+    public interface IServiceHost : IJsonRpcHost
+    {
+        /// <summary>
+        /// Registers a task to be executed when the initialize event is received
+        /// </summary>
+        /// <param name="initializeCallback">Function to execute when the initialize event received</param>
+        void RegisterInitializeTask(Func<InitializeParameters, IEventSender, Task> initializeCallback);
+
+        /// <summary>
+        /// Registers a task to be executed when the shutdown event is received, before the channel
+        /// is closed
+        /// </summary>
+        /// <param name="shutdownCallback">Function to execute when the shutdown request is received</param>
+        void RegisterShutdownTask(Func<object, IEventSender, Task> shutdownCallback);
+    }
+}