functional: replace list.map_with using new functional.map_with.

* specs/functional_spec.yaml (map_with): Specify behaviour of
improved map_with implementation that handles tables.
* lib/std/functional.lua (map_with): Improved implementation of
`list.map_with`.
* lib/std/list.lua (map_with): Deprecate.
* specs/list_spec.yaml (map_with): Adjust accordingly.
* NEWS: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>