Movement Lerp to Hitbox

Movement lerp to hitbox will pull the particle back towards the same part of the model it was spawned on, kind of like a magnet. This can be used to both have particles move to follow animated characters, and to keep normal particle operators from moving the particles away from the model.

According to Chris Green it's meant to work with initializers such as "position on model random", "position on model at specified height", "set hitbox to closest hitbox", that assigns a hitbox index and hitbox relative coordinates to the new particle.