refactor: replace `list.reverse` with `lua.ireverse`.

* specs/lua_spec.yaml (ireverse): Specify behaviour of new
ireverse function.
* specs/list_spec.yaml (relems, reverse): Specify new deprecated
behaviours of these functions.
* lib/std/list.lua (relems, reverse): Deprecated.
* lib/std/base.lua (ireverse): New `__ipairs` aware generator of
new reversed array-part of any table.
* lib/std/lua.lua (ireverse): Export `base.ireverse`.
(monkey_patch): Inject ireverse into given namespace.
* specs/std_spec.yaml (monkey_patch): Adjust accordingly.
* NEWS: Updated.

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