ls: Improve POSIX compatibility for -g and -n.

• Change -g (ignored for BSD 4.3 compatibility since BSD 4.4) to use POSIX semantics of implying -l but omitting the owner's name.

• Change -n to imply -l.

The -o option remains unchanged (POSIX defines -o as a complement to
-g that implies -l but omits group names whereas BSD defines -o to add
file flags to -l). This compromise is the same used by both NetBSD
and OpenBSD.

PR: 70813
Reviewed by: jhb, Pau Amma <pauamma@gundo.com>
Co-authored-by: John Baldwin <jhb@FreeBSD.org>
Differential Revision: https://reviews.freebsd.org/D34747