Water handling: Change Ray cast to OnTriggerEnter/Exit #336

Description

Currently VRSwimDive is raycasting each frame for water height. Let's move it to the collision triggers for improved unity handling.

TODOs

• create a trigger in knee height
• create a trigger in head height
• implement onTriggerEnter/Exit and handle water level value there.
• remove raycast functionality

Reduce on-off bobbing (e.g., in water or when we walk in knee deep and the floor has smaller height differences):

• Implement cooldown before Enter/Exit is recognized (e.g., 0.5f)