Add Garden Top arrows

Two arrows. One above the player, floating. One below the
player, on the ground.

Both arrows use the player's facing angle. Arrows are only
visible to their own player (other players can't see them).

The floating arrow is a papersprite. You can see the arrow
turn with you as you turn your camera.

The grounded arrow is a splat with additive blending. It
tilts to match the slope of the ground you're driving on.