Switched to using a FallbackPackagePathResolver to find the tool dll, because now with Fallback folders, we can have the tool dll in the fallback folder but its assets file in the user nuget cache. This happens because Nuget never writes to the fallback folder, including the tool's assets file that it generates during restore.

TestAssets/TestPackages/dotnet-fallbackfoldertool/Program.cs

@@ -0,0 +1,15 @@
+// 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;
+
+namespace ConsoleApplication
+{
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            Console.WriteLine("Hello Fallback folder World!");
+        }
+    }
+}