Feature request: get all intervals in an interval map that intersect a given one

Example of what I want:

```racket
> (define r (make-interval-map '(((0 . 5) . apple) ((5 . 10) . banana))))
> (interval-map-ref/in r 2 7)
'(((2 . 5) . apple) ((5 . 7) banana))
```

Unresolved questions:

* should we return the entire bounds (i.e. `'(((0 . 5) . apple) ((5 . 10) banana))`) instead?