Tracking issue for release notes of #154620: stabilize new Range type and iterator

[rustbot]

This issue tracks the release notes text for #154620.

cc @pitaj, @tgross35 -- original issue/PR authors and assignees for drafting text

See the forge.rust-lang.org chapter about release notes for an overview of how the release team makes use of these tracking issues.

Release notes text

This section should be edited to specify the correct category(s) for the change, with succinct description(s) of what changed. Some things worth considering:

• Does this need an additional compat notes section?
• Was this a libs stabilization that should have additional headers to list new APIs under Stabilized APIs and Const Stabilized APIs?

# Stabilized APIs
- [`core::range::Range`](https://doc.rust-lang.org/stable/std/range/struct.Range.html)
- [`core::range::RangeIter`](https://doc.rust-lang.org/stable/std/range/struct.RangeIter.html)

Tip

Use the previous releases for inspiration on how to write the release notes text and which categories to pick.

Release blog section

If this change is notable enough for inclusion in the blog post then this section should be edited to contain a draft for the blog post. Otherwise leave it empty.

## New `Range*` types

Many users expect `Range` and related `core::ops` types to be `Copy`, but this is not the case: they implement `Iterator` directly, and [it is a footgun to implement both `Iterator` and `Copy` on the same type](https://rust-lang.github.io/rust-clippy/rust-1.95.0/index.html#copy_iterator) so this has been avoided. [RFC3550] proposed a set of replacement range types that implement `IntoIterator` rather than `Iterator`, meaning they can also be `Copy`. The standard library portion of that RFC is now stable, introducing:

- `core::range::Range`
- `core::range::RangeFrom`
- `core::range::RangeInclusive`
- Associated iterators

A Rust version in the near future will also add `core::range::RangeFull` and `core::range::RangeTo` as re-exports from `core::ops` (these do not implement `Iterator` and already implement `Copy`), and `core::range::legacy::*` as the new home for the current ranges. Range syntax like `0..1` still produces the legacy types for now, but will be updated to `core::range` types in a future edition.

With these stabilizations, it is now possible to store slice accessors in `Copy` types without splitting `start` and `end`:

```rust
use core::range::Range;

#[derive(Clone, Copy)]
pub struct Span(Range<usize>);

impl Span {
    pub fn of(self, s: &str) -> &str {
        &s[self.0]
    }
}
```

Library authors should consider making use of `impl RangeBounds` in public API, which accepts both legacy and new range types. If a concrete type is needed, prefer using new ranges as this will eventually become the default.

[RFC3550]: https://rust-lang.github.io/rfcs/3550-new-range.html

Note

If a blog post section is required the release-blog-post label should be added (@rustbot label +release-blog-post) to this issue as otherwise it may be missed by the release team.