Handle missing closing brackets in turbofish

[estebank]

Like #57817 handles too many closing brackets in type arguments when using turbofish, we should also handle too few closing brackets correctly with an appropriate suggestion (and proper item generation):

fn main() {
    println!("{:?}", vec![1, 2, 3].into_iter().collect::<Vec<usize>());
}

[abonander]

@estebank looks like you got your link syntax turned around

[davidtwco]

I've submitted #57852 for this. It takes the opposite approach to that suggested here, instead of suggesting that extra > characters are added at the end (and making redundant pairs of angle brackets legal), it suggests that unmatched leading < characters are removed.

I think if suggestions are applied with this approach that it ends up with a cleaner result (at the expense of implementation complexity). Happy to scrap that and take the approach suggested here instead if preferred.