Add "dotnet dnx" command as alias for "dotnet tool execute" (#49425)

Author: dsplaisted

src/Cli/Microsoft.TemplateEngine.Cli/Help/HelpBuilder.cs

@@ -43,11 +43,6 @@ public virtual void Write(HelpContext context)
             throw new ArgumentNullException(nameof(context));
         }
 
-        if (context.Command.Hidden)
-        {
-            return;
-        }
-
         foreach (var writeSection in GetLayout(context))
         {
             if (writeSection(context))

src/Cli/dotnet/Commands/Dnx/DnxCommandParser.cs

@@ -0,0 +1,37 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.CommandLine;
+using Microsoft.DotNet.Cli.Commands.Tool;
+using Microsoft.DotNet.Cli.Commands.Tool.Execute;
+
+namespace Microsoft.DotNet.Cli.Commands.Dnx;
+
+internal static class DnxCommandParser
+{
+    public static readonly Command Command = ConstructCommand();
+    public static Command GetCommand()
+    {
+        return Command;
+    }
+
+    private static Command ConstructCommand()
+    {
+        Command command = new("dnx", CliCommandStrings.ToolExecuteCommandDescription);
+        command.Hidden = true;
+
+        foreach (var argument in ToolExecuteCommandParser.Command.Arguments)
+        {
+            command.Arguments.Add(argument);
+        }
+
+        foreach (var option in ToolExecuteCommandParser.Command.Options)
+        {
+            command.Options.Add(option);
+        }
+
+        command.SetAction((parseResult) => new ToolExecuteCommand(parseResult).Execute());
+
+        return command;
+    }
+}

src/Cli/dotnet/Parser.cs

@@ -10,6 +10,7 @@
 using Microsoft.DotNet.Cli.Commands.Build;
 using Microsoft.DotNet.Cli.Commands.BuildServer;
 using Microsoft.DotNet.Cli.Commands.Clean;
+using Microsoft.DotNet.Cli.Commands.Dnx;
 using Microsoft.DotNet.Cli.Commands.Format;
 using Microsoft.DotNet.Cli.Commands.Fsi;
 using Microsoft.DotNet.Cli.Commands.Help;
@@ -66,6 +67,7 @@ public static class Parser
         BuildCommandParser.GetCommand(),
         BuildServerCommandParser.GetCommand(),
         CleanCommandParser.GetCommand(),
+        DnxCommandParser.GetCommand(),
         FormatCommandParser.GetCommand(),
         CompleteCommandParser.GetCommand(),
         FsiCommandParser.GetCommand(),
@@ -313,12 +315,15 @@ public override void Write(HelpContext context)
         {
             var command = context.Command;
             var helpArgs = new string[] { "--help" };
+
+            // custom help overrides
             if (command.Equals(RootCommand))
             {
                 Console.Out.WriteLine(CliUsage.HelpText);
                 return;
             }
 
+            // argument/option cleanups specific to help
             foreach (var option in command.Options)
             {
                 option.EnsureHelpName();