(PUP-2755) Move iterative functions to new api

This moves the iterative functions each, map, reduce, filter, and slice to the new function.
A utility module was added for shared behavior (included in the functions).

This also removes the function stubs for old / renamed iterative functions as these stubs have played out
their role, and it seemed pointless to move them to the new API.
Formatting is just a little off. Either `index += 1` or `index = index + 1`