_dispatchHelpCommand(subcommandName) {
    if (!subcommandName) {
      this.help();
    }
    const subCommand = this._findCommand(subcommandName);
    if (subCommand && !subCommand._executableHandler) {
      subCommand.help();
    }

    // Fallback to parsing the help flag to invoke the help.
    return this._dispatchSubcommand(
      subcommandName,
      [],
      [this._getHelpOption()?.long ?? this._getHelpOption()?.short ?? '--help'],
    );
  }
Invoke help directly if possible, or dispatch if necessary.
e.g. help foo

@private