[DittoTask] If Source is a folder, add all its content as ITaskItem (#14375)

* [DittoTask] If Source is a folder, add all its content as ITaskItem

* [DittoTask] Undoing undo...
* Accidentally hit Cmd+Z and removed an using statement

Co-authored-by: Manuel de la Pena <mandel@microsoft.com>
Co-authored-by: Alex Soto <alex@alexsoto.me>

msbuild/Xamarin.MacDev.Tasks/Tasks/Ditto.cs

@@ -2,6 +2,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
 using Xamarin.Messaging.Build.Client;
 
 namespace Xamarin.MacDev.Tasks
@@ -29,7 +30,16 @@ namespace Xamarin.MacDev.Tasks
 				BuildConnection.CancelAsync (SessionId, BuildEngine4).Wait ();
 		}
 
-		public IEnumerable<ITaskItem> GetAdditionalItemsToBeCopied () => Enumerable.Empty<ITaskItem> ();
+		public IEnumerable<ITaskItem> GetAdditionalItemsToBeCopied ()
+		{	
+			if (!Directory.Exists(Source.ItemSpec))
+				return Enumerable.Empty<ITaskItem> ();
+
+			// TaskRunner doesn't know how to copy directories to Mac but `ditto` can take directories (and that's why we use ditto often).
+			// If Source is a directory path, let's add each file within it as an TaskItem, as TaskRunner knows how to copy files to Mac.
+			return Directory.GetFiles (Source.ItemSpec, "*", SearchOption.AllDirectories)
+				.Select(f => new TaskItem(f));
+		} 
 
 		public bool ShouldCopyToBuildServer (ITaskItem item) => true;