in operator typeguard can widen types

[marekdedic]

Fixes #21732

This PR is a continuation of #39746 - thanks @ShuiRuTian for his work. I have made the branch up-to-date with main and fixed new test breakages. As I am not the original author of most of the changes, I would greatly appreciate a review either from @ShuiRuTian or the maintainers of TS.

Submission containing materials of a third party: @ShuiRuTian

Please verify that:

• There is an associated issue in the Backlog milestone (required)
• Code is up-to-date with the main branch
• You've successfully run gulp runtests locally
• There are new or updated unit tests validating the change

[ghost]

All CLA requirements met.

[marekdedic]

I have signed the CLA, however, I have no idea what to do with the code that is not my own - my layman's interpretation of the CLA is that if @ShuiRuTian signed the CLA as well, than it should all be OK. However, I can't check that he did.

[marekdedic]

Hi, @weswigham
thanks for the tips, I've used one and have some question about the other. Could you please take a look at the comments about the src/compiler/typeTests.ts file by @jakebailey? I'd like to resolve that :)

[HolgerJeromin]

superseded by #50666 ?

[marekdedic]

Yes, superseded. For some (unsolicited) feedback, it's a pretty demotivating contributor experience to have a PR sit and wait for feedback/merge for half a year only to be re-implemented and superseded by a different PR from a project member.

With that said, the other PR is pretty clearly much more expansive and definitely an improvement over this one...