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.CoreServices/Connection/ReliableConnection/IStackSettingsContext.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 System;
+
+namespace Microsoft.SqlTools.CoreServices.Connection.ReliableConnection
+{
+    /// <summary>
+    /// This interface controls the lifetime of settings created as part of the
+    /// top-of-stack API.  Changes made to this context's AmbientData instance will
+    /// flow to lower in the stack while this object is not disposed.
+    /// </summary>
+    internal interface IStackSettingsContext : IDisposable
+    {
+        AmbientSettings.AmbientData Settings { get; }
+    }
+}