CSE machine: animation of spread operator

[martin-henz]

As indicated in #3103

It would be nice to highlight the change of the arity in the CALL instruction using animation.

[alsonleej]

also, [1][2] (array access out of bounds) should push undefined to stash as per Source 4 spec. after implementing in source-academy/js-slang#1750, the animation is still undone (because the "box" has no where to move to)

[alsonleej]

done