Implement shadow filesystems, IFileSystem2.GetSize

src/Umbraco.Core/IO/IFileSystem.cs

@@ -41,4 +41,10 @@ namespace Umbraco.Core.IO
 
         DateTimeOffset GetCreated(string path);
     }
+
+    // this should be part of IFileSystem but we don't want to change the interface
+    public interface IFileSystem2 : IFileSystem
+    {
+        long GetSize(string path);
+    }
 }