Add String#byteindex and String#byterindex

[choznerol]

Fix #2361

In this PR, byteindex and byterindex will become available for String just like index and rindex.

The incorrect output of index and rindex is a separate bug that is tracked by #2360.

Please let me know if equivalent amount of doctest is preferred for all four methods. I was just a bit of worry about being too verbose, so there isn't too many test case for some of them.

[choznerol]

thread 'rustc' panicked at 'no resolutions for a doc link', compiler/rustc_metadata/src/rmeta/encoder.rs:2235:18

The current CI failure seems to be related to rust-lang/rust#109424

[lopopolo]

This change looks good, the functions do what I expect. Thanks for updating the doc tests to have multibyte UTF-8 characters.

I think you've got about the right amount of doc test examples.

Can you add real tests that are a bit more exhaustive? I'd like to see the following coverage:

• all encodings for the receiver
• None given as needle
• Some([])
• ASCII needles
• Binary needles
• UTF-8 needles with multibyte chars
• testing on UTF-8 encoded strings that have binary contents.

[lopopolo]

this looks great.

Once rust-lang/rust#109500 is resolved I think the rustdoc build will be fixed and I'll poke CI to get this merged.

[choznerol]

(Ops sorry I somehow didn't send out the comments yesterday 😅)

Can you add real tests that are a bit more exhaustive? I'd like to see the following coverage:

* all encodings for the receiver
* `None` given as needle
* `Some([])`
* ASCII needles
* Binary needles
* UTF-8 needles with multibyte chars
* testing on UTF-8 encoded strings that have binary contents.

Thanks for the detailed review! I've added the test only for byteindex in d9ce3c8, but not for byterindex to avoid duplication.

[lopopolo]

Thank you this is good to go. It looks like the rust doc folks are making progress on the nightly breakage. I'm following upstream and will poke the build here when nightly is fixed so we can get this merged.

[lopopolo]

nightly rustdoc is fixed, the build is green, merging. thanks for the contribution @choznerol.