modify next_code_point() to accept an Iterator<u8> instead of Iterator<&u8>. Old code that calls it invokes .copied()

[mutantbob]

next_code_point() required an Iterator<Item=&u8> and I only have an Iterator<Item=u8> ; so I have modified next_code_point() to accept an Iterator<Item=u8>. Code that used the old next_code_point() gets modified to call (&mut self.iter).copied().
I threw in some unit tests because I want some confidence that I didn't break anything.
This pull request is an alternate to #95788 . This one is a little less architecturally messy, but will break any external code that was invoking next_code_point().

[rust-highfive]

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with r? rust-lang/libs-api @rustbot label +T-libs-api to request review from a libs-api team reviewer. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

Examples of T-libs-api changes:

• a stabilization of a library feature
• introducing new or changes existing unstable library APIs
• changes to public documentation in ways that create new stability guarantees

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @m-ou-se (or someone else) soon.

Please see the contribution instructions for more information.

[mutantbob]

r? rust-lang/libs-api @rustbot label +T-libs-api

[m-ou-se]

The str_internals feature isn't meant to be used outside the standard library: it's called 'internal', and it doesn't even have a tracking issue. Your changes don't seem to improve the usage of this function within the standard library, with the only motivation coming from external usage of this internal feature.

We can discuss a proposal for adding a public api for this, but we shouldn't change permanently unstable internal-only APIs to suit external needs. Internal functions like these do often have a sub-par design because they only exist for specific needs inside the standard library. Public APIs are held to a higher standard, and need a bit more design and discussion in general.

[mutantbob]

Understood. If there is no support for making this API public I can duplicate the code and figure out how to publish it as a crate for use by applications like mine that need this functionality

[JohnCSimon]

ping from triage:
@mutantbob
Returning to you to address comments.

FYI: when a PR is ready for review, send a message containing
@rustbot ready to switch to S-waiting-on-review so the PR is in the reviewer's backlog.

[bors]

☔ The latest upstream changes (presumably #97729) made this pull request unmergeable. Please resolve the merge conflicts.

[JohnCSimon]

ping from triage:
@mutantbob
seems I forgot to assign back to author....

@rustbot author

[JohnCSimon]

@mutantbob
Ping from triage: I'm closing this due to inactivity, Please reopen when you are ready to continue with this.
Note: if you do please open the PR BEFORE you push to it, else you won't be able to reopen - this is a quirk of github.
Thanks for your contribution.

@rustbot label: +S-inactive