Introducing .flatMapN(f) as a shorthand for .mapN(f).flatten

[domaspoliakas]

Hello 👋 this follows from my question on discord and is basically the title.

I find myself doing .mapN(f).flatten very frequently and I think it'd be nice to have a .flatMapN for this scenario.

I am told this was rejected in the past, but I could not find a past issue for this and so I was hoping I could reopen a discussion.

Thanks!

[joroKr21]

I've thought about this too. The only potential issue I see is the cost in terms of increased Jar size (because that would add not 1 but 22 extra methods). However I'm not sure that's really a concern because #3871 didn't generate much interest.

[domaspoliakas]

Given that there were no nays yet, I shall get started on making this. Is that alright?