Implement std::iter::FromIterator<char> for Box<str>

[Duddino]

This would allow to construct a Box from an iterator, example: let string: Box<str> = (0..5).map(|_| '☺').collect();

This issue has been assigned to @Duddino via this comment.

[jonas-schievink]

Did you mean FromIterator?

[Duddino]

Yes thank you

[bluss]

The workaround to use until then is (0..5).map(|_| '☺').collect::<String>().into_boxed_str() which will be equivalent to the eventual solution in behaviour and performance.

[Duddino]

@rustbot claim

[Duddino]

I made the change, should I proceed with a PR? Sorry if it's a stupid question, but it's my first issue

[bluss]

@Duddino I think you can. The equivalent thing for Box<[T]> was in #55843 and the process should be similar.

If you are curious, bigger changes - not this one - in Rust might require an RFC -- see the contributing file.

[Duddino]

@Blussi Thank you!

[bluss]

PR is #65168