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.

まず、この issue の議論と参照されている LSU fork の変更を確認し、そこで `\u0026` が `pictures` または `combined` にどのように置き換えられたかを比較します。完了とするには、CodeWorld でこの演算子を非推奨にするかどうか、またどのように非推奨にするかについて結論を出す必要があります。対象ファイルやテストは特定されていません。

索引モデルが issue の本文から書いたものです。