Provide suggestion to dereference closure tail if appropriate

When encoutnering a case like

```rust
//@ run-rustfix
use std::collections::HashMap;

fn main() {
    let vs = vec![0, 0, 1, 1, 3, 4, 5, 6, 3, 3, 3];

    let mut counts = HashMap::new();
    for num in vs {
        let count = counts.entry(num).or_insert(0);
        *count += 1;
    }

    let _ = counts.iter().max_by_key(|(_, v)| v);
```
produce the following suggestion
```
error: lifetime may not live long enough
  --> $DIR/return-value-lifetime-error.rs:13:47
   |
LL |     let _ = counts.iter().max_by_key(|(_, v)| v);
   |                                       ------- ^ returning this value requires that `'1` must outlive `'2`
   |                                       |     |
   |                                       |     return type of closure is &'2 &i32
   |                                       has type `&'1 (&i32, &i32)`
   |
help: dereference the return value
   |
LL |     let _ = counts.iter().max_by_key(|(_, v)| **v);
   |                                               ++
```

Fix #50195.

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