Fix P2P migration

Fixes #4269 by deep cloning the MsbuildTemplateProject for each P2P reference. Add test which migrates and builds P2P references.

TestAssets/TestProjects/TestAppDependencyGraph/ProjectA/Program.cs

@@ -11,7 +11,7 @@ namespace TestApp
         public static int Main(string[] args)
         {
             Console.WriteLine("This string came from ProjectA");
-            return 100;
+            return 0;
         }
     }
 }