Show help output when there are unmatched tokens passed to update-dependencies CLI (#6402)

Co-authored-by: Matt Thalman <mthalman@microsoft.com>

Author: lbussell

eng/update-dependencies/Program.cs

@@ -1,8 +1,11 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using System.CommandLine;
+using System.CommandLine.Help;
 using System.CommandLine.Hosting;
+using System.IO;
 using System.Net.Http;
 using Dotnet.Docker;
 using Microsoft.DotNet.DarcLib;
@@ -22,8 +25,20 @@
 var config = new CommandLineConfiguration(rootCommand);
 
 config.UseHost(
-    _ => Host.CreateDefaultBuilder(),
-    host => host.ConfigureServices(services =>
+    hostBuilderFactory: unmatchedArgs =>
+        {
+            if (unmatchedArgs.Length > 0)
+            {
+                var helpBuilder = new HelpBuilder();
+                using var stringWriter = new StringWriter();
+                helpBuilder.Write(rootCommand, stringWriter);
+                Console.WriteLine(stringWriter.ToString());
+                throw new InvalidOperationException($"Unmatched tokens: {string.Join(" ", unmatchedArgs)}");
+            }
+
+            return Host.CreateDefaultBuilder();
+        },
+    configureHost: host => host.ConfigureServices(services =>
         {
             services.AddSingleton<IBasicBarClient>(_ =>
                 new BarApiClient(null, null, disableInteractiveAuth: true));