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/ISqlConnectionFactory.cs

@@ -0,0 +1,20 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System.Data.Common;
+
+namespace Microsoft.SqlTools.CoreServices.Connection
+{
+    /// <summary>
+    /// Interface for the SQL Connection factory
+    /// </summary>
+    public interface ISqlConnectionFactory
+    {
+        /// <summary>
+        /// Create a new SQL Connection object
+        /// </summary>
+        DbConnection CreateSqlConnection(string connectionString);
+    }
+}