display CommandParsingException gracefully (#5493)

* display CommandParsing gracefully

This set of changes handles CommandParsingException gracefuly (so as not to show the user a stack trace) and generalizes graceful exception display somewhat away from being type-specific.

* fix compile error by inlining constant

* remove unused test logging

test/dotnet-new.Tests/NewCommandTests.cs

@@ -0,0 +1,26 @@
+// 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 FluentAssertions;
+using Microsoft.DotNet.Tools.Test.Utilities;
+using System;
+using System.Linq;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Microsoft.DotNet.New.Tests
+{
+    public class NewCommandTests
+    {
+        [Fact]
+        public void WhenSwitchIsSkippedThenItPrintsError()
+        {
+            var cmd = new DotnetCommand().Execute("new Web1.1");
+
+            cmd.ExitCode.Should().NotBe(0);
+            
+			cmd.StdErr.Should().Be("Unrecognized command or argument 'Web1.1'");
+            cmd.StdOut.Should().Be("Specify --help for a list of available options and commands.");
+		}
+	}
+}