b435960c4c
`Split*::as_str` refactor I've made this patch almost a year ago, so the rename and the behavior change are in one commit, sorry 😅 This fixes #84974, as it's required to make other changes work. This PR - Renames `as_str` method of string `Split*` iterators to `remainder` (it seems like the `as_str` name was confusing to users) - Makes `remainder` return `Option<&str>`, to distinguish between "the iterator is exhausted" and "the tail is empty", this was [required on the tracking issue](https://github.com/rust-lang/rust/issues/77998#issuecomment-832696619) r? `@m-ou-se`