Rollout rock improvements

I generally consider my implementation of the rollout rock to be poor and in need of a rethink, but here are some QOL changes that shouldn't break scripts that are used to its current behavior.

• The rock no longer struggles to start accelerating at certain angles (related to #451 (closed))
• Carrying a player onto a rollout rock no longer leaves them in their ride state
• Tweaked its dispoffset, which might alleviate some sprite sorting issues
• Changes the player's camera angle when sprung horizontally (resolves #445 (closed))
• Works better in reverse gravity (resolves #221 (closed))
• Controls properly in 2D mode (resolves #532 (closed))