Auto merge of #134929 - compiler-errors:style-edition-2024, r=ytmimi

Stabilize `style_edition = "2024"` in-tree

This PR stabilizes the `style_edition` flag in rustfmt.

**Why am I doing this in-tree?** The beta release cut is imminent (according to forge, on January 3) and this is the most lightweight approach to getting this flag stable on nightly. It's imperative (as far as I can tell -- `@traviscross` can verify or disagree) that we stabilize the `style_edition` flag so that users can control their style edition separately from the edition.

I'm happy to move this PR to the rustfmt repo and subsequently prepare a subtree sync if someone on `@rust-lang/rustfmt` believes that we should get this landed on the rustfmt side then synced. If this is the right recourse, I'd like to note that this is still quite time-sensitive. However, I'm happy to dedicate time to get this done if necessary, since I'd really like to un-jeopardize the style edition.

Tracking:

- rust-lang/rust#123799

Author: bors