Command and option descriptions are not easily localized

[jonsequitur]

The incoming mechanisms for setting the culture via environment variables and directives (#951) don't allow a straightforward way to localize descriptions, because the parser is configured before the middleware that sets the culture gets executed.

Example:

        static void Main(string[] args)
        {
            // OOPS: Environment variable isn't set yet, and neither is the current culture the one we'll be using at invocation time
            var description = Environment.GetEnvironmentVariable("DOTNET_SYSTEM_GLOBALIZATION_CULTURE") switch
            {
                "es-ES" => "hola",
                _ => "hello"
            };

            var option1 = new Option<string>("-x", description);

            new RootCommand
            {
                option1
            }.Invoke(args);
        }

[fredrikhr]

I wonder whether we'd approach this problem by adding a LocalizedHelpBuilder that derives from the deafult HelpBuilder and uses an ILocalizer from the Microsoft.Extensions.Localization. In such a case the Description of a Command/Option/Argument would be the invariant string/key passed to the ILocalizer and would either return the invariant or localized string in the output

If we don't want to add dependency to Microsoft.Extensions.Localization we could introduce a new System.CommandLine.Localization package (similar to the System.CommandLine.Hosting package). On the other extreme side, we could make the default Help builder use localization by default.

[fredrikhr]

I am currently working on #1013 which is still work in progress which will introduce a new package System.CommandLine.Localization and add a new extension method UseLocalization to CommandLineBuilder.