When encountering `for<'a>` in closure declaration, try to provide structured suggestion to use a binding with a type

[estebank]

Code

fn main() {
    //let cl: for<'a> fn(&'a str) -> (&'a str, &'a str) = |x| { x.split_at(0) };
    let cl = for<'a> |x: &'a str| -> (&'a str, &'a str) { x.split_at(0) };
    let (_x, _y) = cl("42");
}

Current output

error[E0658]: `for<...>` binders for closures are experimental
 --> f83.rs:3:14
  |
3 |     let cl = for<'a> |x: &'a str| -> (&'a str, &'a str) { x.split_at(0) };
  |              ^^^^^^^
  |
  = note: see issue #97362 <https://github.com/rust-lang/rust/issues/97362> for more information
  = help: add `#![feature(closure_lifetime_binder)]` to the crate attributes to enable
  = help: consider removing `for<...>`

Desired output

error[E0658]: `for<...>` binders for closures are experimental
 --> f83.rs:3:14
  |
3 |     let cl = for<'a> |x: &'a str| -> (&'a str, &'a str) { x.split_at(0) };
  |              ^^^^^^^
  |
  = note: see issue #97362 <https://github.com/rust-lang/rust/issues/97362> for more information
  = help: add `#![feature(closure_lifetime_binder)]` to the crate attributes to enable
  = help: consider setting the binding type instead
  |
3 -     let cl = for<'a> |x: &'a str| -> (&'a str, &'a str) { x.split_at(0) };
3 +     let cl: for<'a> fn(&'a str) -> (&'a str, &'a str) = |x| { x.split_at(0) };
  |

Rationale and extra context

Although the feature is unstable, someone trying to deal with lifetime errors might accidentally arrive to this code, but the feature gate doesn't actually provide reasonable guideline on what to do instead.

Other cases

Rust Version

1.97

Anything else?

Noticed while looking at #58525.