API docs for NoReturn and Void are missing

[straight-shoota]

The stdlib API documentation has no entry for NoReturn and Void.
They are special types defined by the compiler, but we usually document those in the API docs as well for completeness.
The language specification has a section about it: https://crystal-lang.org/reference/1.7/syntax_and_semantics/return_types.html

There's a significant roadblock: NoReturn and Void are special kinds of types and cannot be reopened in code which would be necessary to attach a doc comment. So we'll probably need to implement some kind of workaround in the doc generator to make it possible. Maybe something similar to #8327.

Edit: Added Void (originally, it was only about NoReturn).

[devnote-dev]

This should also include Void which is mentioned in the C Bindings section next to NoReturn.

[HertzDevil]

#8422 is also a possible solution for NoReturn (you could define class methods on NoReturn just fine so there is a use case for that).