retain postfix node in type section typed AST, with docgen fix

[metagn]

Continued from #23096 which was reverted due to breaking a package and failing docgen tests. Docgen should now work, but a PR is still pending for the package: SciNim/Unchained#45 has been merged

[metagn]

CI now passes

[Araq]

Superb work, but how hard would it be for the doc gen to not render the export markers? Only public symbols are visible in the docs anyway so the export marker is redundant and it's bit uglier with them.

[metagn]

Apparently the docgen just renders the AST, we could add a TRenderFlag that never renders postfixes. This would also make object fields not render postfixes anymore (right now they do). Edit: Added renderNoPostfix, but it has an exception for fields

That being said I only now realized let/const/proc also do not retain postfix nodes. I can do these as well but they have a chance of breaking packages again (especially proc), should they go in a separate PR after this one?

[Araq]

should they go in a separate PR after this one?

Yes, please.

[github-actions]

Thanks for your hard work on this PR!
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