Tracking issue for release notes of #134340: Stabilize `num_midpoint_signed` feature

[rustbot]

This issue tracks the release notes text for #134340.

Steps

• Proposed text is drafted by PR author (or team) making the noteworthy change.
• Issue is nominated for release team review of clarity for wider audience.
• Release team includes text in release notes/blog posts.

Release notes text

The responsible team for the underlying change should edit this section to replace the automatically generated link with a succinct description of what changed, drawing upon text proposed by the author (either in discussion or through direct editing).

# Const Stabilized APIs
- [`<iN>::midpoint`](https://doc.rust-lang.org/std/primitive.isize.html#method.midpoint)

Tip

Use the previous releases categories to help choose which one(s) to use.
The category will be de-duplicated with all the other ones by the release team.

More than one section can be included if needed.

Release blog section

If the change is notable enough for inclusion in the blog post, the responsible team should add content to this section.
Otherwise leave it empty.

cc @Urgau, @dtolnay -- origin issue/PR authors and assignees for starting to draft text

[scottmcm]

I don't think this needs more than the usual stabilization mention.

If you wanted to mention more, you could say something like

You can now replace (a + b) / 2 with a.midpoint(b), which works correctly even in places where a + b would have overflown.

[pthariensflame]

This is a full stabilization, not just a const-stabilization, so it should move sections.