gh-104010: Separate and improve docs for `typing.get_origin` and `typing.get_args` (#104013)

* separate documentation and examples for both functions
* add examples demonstrating behaviour with unsupported types
* document return value of `get_origin` for `ParamSpecArgs` and `ParamSpecKwargs` instances

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>