Rollup merge of #67595 - ohadravid:impl-trait-does-not-live-long-enough, r=estebank

Rollup merge of #67595 - ohadravid:impl-trait-does-not-live-long-enough, r=estebank

Suggest adding a lifetime constraint for opaque type

Fixes #67577, where code like this:

```
struct List {
  data: Vec<String>,
}
impl List {
  fn started_with<'a>(&'a self, prefix: &'a str) -> impl Iterator<Item=&'a str> {
    self.data.iter().filter(|s| s.starts_with(prefix)).map(|s| s.as_ref())
  }
}
```

will show this error:
```
   Compiling playground v0.0.1 (/playground)
error[E0597]: `prefix` does not live long enough
 --> src/lib.rs:6:47
  |
5 |   fn started_with<'a>(&'a self, prefix: &'a str) -> impl Iterator<Item=&'a str> {
  |                   -- lifetime `'a` defined here     --------------------------- opaque type requires that `prefix` is borrowed for `'a`
...
```

but without suggesting the lovely `help: you can add a constraint..`.

r? @estebank