Evaluate a term under a ground substitution using magic-ev-fncall.
(magic-ev term alist state hard-error-returns-nilp aokp)
evaluates the given term under the alist mapping variables to values. Functions within the term are evaluated using magic-ev-fncall and the values returned are the same as for magic-ev-fncall, that is,
(mv NIL value)
on success or
(mv T error-msg)