reblessive regression: rely on item bounds of not-yet-defined opaque types 

https://crater-reports.s3.amazonaws.com/pr-133502-2/try%23da0a4799770027c4c578bf48cdb390acfde09023/reg/reblessive-0.4.3/log.txt

```rust
async fn mirror<T>(t: T) -> T {
    let x = Box::pin(mirror(String::new())).await;
    let recur = x.len();
    
    t
}
```

Recursive non-defining use. Old solver can solve `{opaque#0}::<String>: Future<Output = ?x>` and constrains the type of variable `x`.