Catalog `style_edition=2027` formatting differences

[ytmimi]

Tracking issue documenting style_edition=2027 changes.

[ytmimi]

[!IMPORTANT] This change was reverted in https://github.com/rust-lang/rustfmt/pull/6595 because style-edition=2024 had already been released before we could defer the change to style-edition=2027.

---

Reverted Change

### Break function return types before `->` instead of breaking between `()` for zero argument functions

Related PR: https://github.com/rust-lang/rustfmt/pull/6362

style_edition == 2027

pub fn parse_conditional<'a, I: 'a>()
-> impl Parser<Input = I, Output = Expr, PartialState = ()> + 'a
where
    I: Stream<Item = char>,
{
}

style_edition <= 2024

pub fn parse_conditional<'a, I: 'a>(
) -> impl Parser<Input = I, Output = Expr, PartialState = ()> + 'a
where
    I: Stream<Item = char>,
{
}

[ytmimi]

TODO: Document https://github.com/rust-lang/rustfmt/pull/6572

[ytmimi]

TODO: Document https://github.com/rust-lang/rustfmt/pull/6594