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/ConnectionUtils.cs

@@ -0,0 +1,31 @@
+//
+// 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;
+using Microsoft.Data.SqlClient;
+using Microsoft.SqlTools.CoreServices.Connection.ReliableConnection;
+
+public static class ConnectionUtils
+{
+    public static SqlConnection GetAsSqlConnection(DbConnection connection)
+    {
+        SqlConnection sqlConn = connection as SqlConnection;
+        if (sqlConn == null)
+        {
+            // It's not actually a SqlConnection, so let's try a reliable SQL connection
+            ReliableSqlConnection reliableConn = connection as ReliableSqlConnection;
+            if (reliableConn == null)
+            {
+                // If we don't have connection we can use with SMO, just give up on using SMO
+                return null;
+            }
+
+            // We have a reliable connection, use the underlying connection
+            sqlConn = reliableConn.GetUnderlyingConnection();
+        }
+        return sqlConn;
+    }
+}