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/IEventSender.cs

@@ -0,0 +1,23 @@
+//
+// 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.Contracts;
+
+namespace Microsoft.SqlTools.Hosting.Protocol
+{
+    /// <summary>
+    /// Interface for objects that can send events via the JSON RPC channel
+    /// </summary>
+    public interface IEventSender
+    {
+        /// <summary>
+        /// Sends an event over the JSON RPC channel
+        /// </summary>
+        /// <param name="eventType">Configuration of the event to send</param>
+        /// <param name="eventParams">Parameters for the event to send</param>
+        /// <typeparam name="TParams">Type of the parameters for the event, defined in <paramref name="eventType"/></typeparam>
+        void SendEvent<TParams>(EventType<TParams> eventType, TParams eventParams);
+    }
+}