Implement piercing projectiles

[aspin]

notes from rapier dev:

- The pierceable object could be a sensor. That way it will never result in a collision response (though that means you won't get any contacts, even with the objects that are not supposed to pierce it).
- Or you could check for all the contact pairs with your piercing object after a timestep. If there is a pair with active contacts that involve an object that can pierce it, then you can remove the piercing object. Though this means that for one timestep there will be a collision repsonse between the pierceable object and the object that pierces it.
- Or you could disable the collision solver (using the collider's solver_groups) for collision pairs that involve your pierceable object and the ones that can pierce it. That way you keep the collision response between your pierceable object and all the other objects, but won't have any collision response between the pierceable object and the ones that can pierce it. Then after the timestep is complete, you can check the contacts between your pierceable object and the ones that can pierce it, and do whatever you need to do as a result of thie piercing.```