opeators: add a MapError opeator

[JCSooHwanCho]

Description

This PR adds MapError Operator, which is transforms error upstream emits

Checklist

• this PR is based on the main branch and is up-to-date, if not please rebase your branch on the top of main
• the commits inside this PR have explicit commit messages
• unit tests cover the new feature or the bug fix
• the feature is documented in the README.md if it makes sense
• the CHANGELOG is up-to-date

[twittemb]

Hi @JCSooHwanCho

Thanks for this PR.

Mmmmh, I'm not sure if this is useful to be able to map the error since an AsyncSequence, unlike a Combine publisher, is not parametrised by a Failure type.

In the end we still have to handle all kinds of Errors in the catch section. The mapError does not bring type safety here.

Do you see a big advantage to that ?

[JCSooHwanCho]

@twittemb I needed some functionality that catch some error and change it to another Error. so first I thought was mapError operator in Combine, implement and use it. but by your comment, catch operator in RxSwift is rather nicer than mapError with AsyncSequence case.

[twittemb]

@JCSooHwanCho I have introduced a .mapToResult operator (main branch), it might be more versatile