Consider upstreaming deprecation of & from LSU fork

I noticed that @alphalambda removed the `&` operator from their standard library, in favor of `pictures` (renamed to `combined` in that fork). I've had similar thoughts, and I wonder if I ought to do the same thing (slowly, with a VERY long deprecation cycle) in my own copy.

I think the issue is that students find `&` to be too much like English, and not enough like a mathematical operator. That leads them to have incorrect expectations that it can be used in all places where they want multiple things. I've seen students try to use `&` to separate animations, items in a list, and so on.

I definitely haven't decided to do this. I think I'll wait to discuss with @alphalambda after it's been used there for a while. It would be a shame to do such a disruptive deprecation, only to learn that it doesn't help! Just creating the issue to capture discussion and track the decision-making.

Comienza revisando la discusión de este issue y el cambio referenciado del fork de LSU; después, compara cómo se reemplazó `\u0026` por `pictures` o `combined` allí. Para darlo por terminado, sería necesario tomar una decisión definitiva sobre si CodeWorld debería marcar el operador como obsoleto y cómo hacerlo; no se han identificado archivos objetivo ni pruebas.

Escrito por el modelo de indexación a partir del texto del issue.