Consider removing `Command.AddOption`, `Command.AddCommand`, and `Command.AddArgument` because they're redundant with `Add`

[jonsequitur]

        // You have both Add(Option) and AddOption(Option).  Pick a paradigm.  I recommend "AddOption", since you need "AddGlobalOption" as different.
        // Also applies to Argument and Command as only having AddArgument and AddCommand.
        public void Add(Option option);
        public void Add(Argument argument);
        public void Add(Command command);
        public void AddArgument(Argument argument);
        public void AddCommand(Command command);

[KalleOlaviNiemitalo]

This was done in #1989.