Remove System.CommandLine dependency.

Also removed the dependency on Microsoft.Extensions.CommandLineUtils.Sources NuGet package and instead just checking the source files into our repo as internal classes.

Fix #2526

src/dotnet/CommandLine/CommandParsingException.cs

@@ -0,0 +1,18 @@
+// 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 Microsoft.DotNet.Cli.CommandLine
+{
+    internal class CommandParsingException : Exception
+    {
+        public CommandParsingException(CommandLineApplication command, string message)
+            : base(message)
+        {
+            Command = command;
+        }
+
+        public CommandLineApplication Command { get; }
+    }
+}