Feature request: ContactPairView::other_collider

Hi!

In the documentation I saw this example:

```rust
let other_collider = if contact_pair.collider1() == entity {
contact_pair.collider2()
} else {
contact_pair.collider1()
};
```

I thought that I'd suggest a method on `ContactPairView`; `other_collider`

Disclaimer: I'm just learning rust so this might be bad code. I'd appreciate any feedback.

Anyway, here's the idea code:

```rust
impl<'a> ContactPairView<'a> {

...

pub fn other_collider(&self, entity: Entity) -> Option {
if entity == self.collider1() { return Some(self.collider2()); };
if entity == self.collider2() { return Some(self.collider1()); };
None
}
}
```

Thoughts? :)