Add new command class framework for easier testing (#17851)

* Add new command class framework for easier testing

* Add better test coverage

* Surface exception message

* textwrap.dedent

* remove unnecessary list

* Remove type check

* helper attribute variable name

* Rename helper attribute

* Simplify and statement

* Do some de-nesting

* Take default suggestion

* Add a __call__ method to the command parser

* subclass -> member

* Remove requirement that requied=False on optionals

* remove useless is_command_option

* Use global 'register' for special types

* Use a class for metadata optiona args

* Revert option args to class