io::ErrorKind should suggest c&p current list of kinds into test cases

[ijackson]

The introduction of the perma-usntable Uncategorized is IMO correct, but it is causing quite a lot of trouble for people (see comments in #86442 for example). One difficulty is that people experiencing breakage aren't given clear guidance on how to fix their code, which is a poor UX.

As I wrote in #79965 (comment) I think the right answer in some cases (eg for a thorough test case) is to cut and paste the list of currently-stable kinds from the stdlib docs into one's codbase. This is counterintuitive but IMO correct.

I think it would be useful to recommend this somewhere in the docs for io::ErrorKind. If the community agrees I will send an MR. But I thought I would test the waters with this issue, first.

[ijackson]

@rustbot modify labels +T-libs-api +A-io