Allow migration of sln files (#4949)

* WIP Migrate sln files

* WIP add reference to redist

* Adding tests and fixing a few bugs

* Fix some tests

* Remove use of DeepClone

* Fix test build errors

* Fix more tests

TestAssets/TestProjects/TestAppWithSlnAndMultipleProjects/TestApp/Program.cs

@@ -0,0 +1,17 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Diagnostics;
+
+namespace TestApp
+{
+    public class Program
+    {
+        public static int Main(string[] args)
+        {
+            Console.WriteLine(TestLibrary.Helper.GetMessage());
+            return 100;
+        }
+    }
+}