Rename `recursive_iterator` to `recursive_generator`

[evhub]

It's a much clearer name for describing what the function does. The old name would stick around but be deprecated and not work in --strict mode as we've done previously for of, datamaker, and prepattern.

[evhub]

I feel like recursive_generator still kinda sucks as a name. Worth maybe aliasing again and coming up with a better long-term name.