Gets ground collision data for the wheel.
If the wheel collides with something, returns true and fills the hit structure. If the wheel
is not colliding, returns false and leaves hit structure unchanged.
The reported hit is always the closest one. Because the tire friction model does not automatically
respond to other PhysicMaterials, any simulation of different ground materials must be done
manually by adjusting forwardFriction and sidewaysFriction based on collider's
material returned here.