use_tidy_base_pipe()

[hadley]

Wrap up the code we used in purrr to make it easy for other packages to use the base pipe in examples.

A stretch goal would be to also figure out the regexp to replace %>% with |> inside roxygen comments and vignettes.

[jennybc]

I'm putting the tidyverse dev day label on this, not because I think it can be settled in one day. Rather, this would be a research project. Some TODOs to get thing started:

• Gather links to the relevant purrr PR(s).
• Study the purrr example and enumerate the main "moves" that are necessary.
• (Maybe?) create a draft PR that starts to chip away at the problem.

[hadley]

We've waited so long it's not really worth doing this; we might as well just wait another 6 months until we can use R 4.1 eveywhere.