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.DataProtocol.Contracts/Connection/ConnectionChangedNotification.cs

@@ -0,0 +1,19 @@
+//
+// 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.DataProtocol.Contracts.Connection
+{
+    /// <summary>
+    /// ConnectionChanged notification mapping entry 
+    /// </summary>
+    public class ConnectionChangedNotification
+    {
+        public static readonly
+            EventType<ConnectionChangedParams> Type =
+            EventType<ConnectionChangedParams>.Create("connection/connectionchanged");
+    }
+}