(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.
it should now, it was not always the case... (fixing)