Add result_and_then_ok lint

[printfn]

changelog: add result_and_then_ok lint to warn about result.and_then(|o| Ok(x)) and suggest replacing with result.map(|o| x).

[printfn]

Thanks for reviewing! I've now re-added the regression tests (with an allow attribute), renamed the variables and hopefully fixed the documentation code.

[flip1995]

Thanks for implementing this lint so fast after the other was finished!

You should be able to share most of the Code of the option_and_then_some lint. Please deduplicate as much code as possible and implement the two lints in one function. (That's actually the tricky part of adding this lint 😉)

[bors]

☔ The latest upstream changes (presumably #4498) made this pull request unmergeable. Please resolve the merge conflicts.

[hellow554]

@printfn please edit your first post and add one of the closing keywords github provides together with the issue number 4412, e.g.

closes #4412

[flip1995]

implemented in #5529