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/Utility/ServiceProviderNotSetException.cs

@@ -0,0 +1,17 @@
+//
+// 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 Microsoft.SqlTools.Hosting.v2;
+
+namespace Microsoft.SqlTools.Hosting.Utility
+{
+    public class ServiceProviderNotSetException : InvalidOperationException {
+
+        public ServiceProviderNotSetException()
+            : base(SR.ServiceProviderNotSet) {
+        }
+    }
+}