Add various forms of friction to swimming to prevent unlimited speed gain

[GTcreyon]

Three forms of friction are applied:

• Soft speed cap. Prevent the player from increasing their overall speed while over the speed cap.
• Perpendicular friction. When the player is moving in a direction different to the current direction of motion, apply friction on the perpendicular axis so they don't continue to drift in that direction.
• Radial friction. When the player is above the speed cap, apply friction to reduce them to the cap.