Extract collision detection logic from Actor

To be able to add new types of `SceneObjects` that support collision detection without duplicating code, the collision detection logic in `Actor` needs to be extracted.

We probably need a new protocol something like this:

```swift
internal protocol Collidable {
var isCollisionDetectionEnabled: Bool { get set }
var rectForCollisionDetection: Rect { get }
}
```

Collision events also need to be extracted from ActorEventCollection.