Tracking issue for release notes of #148051: Stabilize Frontmatter

This issue tracks the release notes text for #148051.

cc @epage, @davidtwco -- 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?

# Language
- [Stabilize Frontmatter](https://github.com/rust-lang/rust/pull/148051)

[!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.

## Cargo script support

Cargo scripts are Rust files with their `Cargo.toml` embedded inside of them using a new Rust syntax called "frontmatter".
This is helpful for
- Self-contained reproduction cases for bug reports
- Communicating using code snippets that use dependencies in blog posts, chat, books, etc
- Exploratory programming

Example:
~~~rust
#!/usr/bin/env cargo
---
[dependencies]
rand = "0.9"
---

use rand::Rng;

fn main() {
    let mut rng = rand::rng();
    let random_number: u32 = rng.random();
    println!("Random number: {random_number}");
}
~~~

[!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.

Read the forge.rust-lang.org release-notes chapter and previous releases for category conventions. Review the release notes and blog sections in this issue, then confirm the text accurately describes #148051 and add any needed compatibility or API headings; leave the blog section empty if it is not notable enough.