Playlab go to xy

Necessary for animation in MSM (particularly quadratic motion and nonlinear acceleration). I don’t expect this
block to be used directly by students (at least not in any of our
current courses).
Nit: prefer one of the following styles (i like first best)
```
Studio.stop({
  'spriteIndex': opts.spriteIndex,
  'dontResetCollisions': samePosition
});

Studio.stop({'spriteIndex': opts.spriteIndex,
  'dontResetCollisions': samePosition});