Fix 'security.bsd.see_jail_proc' by using cr_bsd_visible()

As implemented, this security policy would only prevent seeing processes
in sub-jails, but would not prevent sending signals to, changing
priority of or debugging processes in these, enabling attacks where
unprivileged users could tamper with random processes in sub-jails in
particular circumstances (conflated UIDs) despite the policy being
enforced.

PR: 272092
Reviewed by: mhorne
MFC after: 2 weeks
Sponsored by: Kumacom SAS
Differential Revision: https://reviews.freebsd.org/D40628

(cherry picked from commit 5817169bc4a06a35aa5ef7f5ed18f6cb35037e18)