Treat /? the same as --help (#5285)

* Fixes issue 4539

* Support -?

src/dotnet/CommandLine/CommandLineApplication.cs

@@ -148,7 +148,12 @@ namespace Microsoft.DotNet.Cli.CommandLine
                 var arg = args[index];
 
                 bool isLongOption = arg.StartsWith("--");
-                if (isLongOption || arg.StartsWith("-"))
+                if (arg == "-?" || arg == "/?")
+                {
+                    command.ShowHelp();
+                    return 0;
+                }
+                else if (isLongOption || arg.StartsWith("-"))
                 {
                     CommandOption option;
                     var result = ParseOption(isLongOption, command, args, ref index, out option);

src/dotnet/Program.cs

@@ -118,7 +118,9 @@ namespace Microsoft.DotNet.Cli
                         PrintInfo();
                         return 0;
                     }
-                    else if (IsArg(args[lastArg], "h", "help"))
+                    else if (IsArg(args[lastArg], "h", "help") || 
+                        args[lastArg] == "-?" ||
+                        args[lastArg] == "/?")
                     {
                         HelpCommand.PrintHelp();
                         return 0;

test/dotnet-help.Tests/GivenThatIWantToShowHelpForDotnetCommand.cs

@@ -56,6 +56,8 @@ Advanced Commands:
         [Theory]
         [InlineData("--help")]
         [InlineData("-h")]
+        [InlineData("-?")]
+        [InlineData("/?")]
         public void WhenHelpOptionIsPassedToDotnetItPrintsUsage(string helpArg)
         {
             var cmd = new DotnetCommand()

test/dotnet-sln-add.Tests/GivenDotnetSlnAdd.cs

@@ -182,6 +182,8 @@ EndGlobal
         [Theory]
         [InlineData("--help")]
         [InlineData("-h")]
+        [InlineData("-?")]
+        [InlineData("/?")]
         public void WhenHelpOptionIsPassedItPrintsUsage(string helpArg)
         {
             var cmd = new DotnetCommand()