awk(1): Fix typo

This is from the Advanced UNIX Programming Course (Fall’23) at NTHU.

MFC after: 3 days
Pull Request: https://github.com/freebsd/freebsd-src/pull/928

Remove $FreeBSD$: two-line nroff pattern

Remove /^\.\\"\n\.\\"\s*\$FreeBSD\$$\n/

awk: Document deprecated behavior of hex constants and locales.

FreeBSD will convert "0x12" from hex and print it as 18. Other awks will
convert it to 0. This extension has been removed upstream, and will be
removed in FreeBSD 14.0.

FreeBSD used to set the locale on startup, and make the ranges use that
locale. This lead to weird results like "[A-Z]" matching lower case
characters in some locales. This bug has been fixed.

MFC After: 3 days
Sponsored by: Netflix

awk: Flag -Ft as deprecated behavior

Upstream is poised to deprecate the -Ft wart in one true awk. None of
the other awks do this, and the gawk maintainer says that he's had no
requests for it in gawk in 30 years maintaining it. github can find a
few instances of it in the wild. As such, warn that it's deprecated and
will go away in the future.

MFC After: 3 days
Sponsored by: Netflix

awk: Add more details top the FS variable

The current description of the FS is true, but only part of the
truth. Add information about single characters and note that FS="" is
undefined by the standard, though the two other awk implenetations (mawk
and gawk) also have this interpretation.

PR: 226112
Sponsored by: Netflix

awk(1): use -version instead of -V

-V is OpenBSD specific, use -version instead.

While here, fix issue reported by mandoc lint and drop nonexistent
script(7) reference.

PR: 247004
Reviewed by: 0mp, markj
Differential Revision: https://reviews.freebsd.org/D25164

Implement gawk multiple-arg extension to and, or, and xor.

gawk allows multiple arguemnts to bit-wiste and, or and xor
functions. Implement an arbitrary number of arguments for these
functions. Also, use NULL in preference to 0 to match rest of file.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D12361

Import the awk(1) manpage from OpenBSD

As discussed during AsiaBSDcon devsummit, import the manpage from OpenBSD which
is has been rewritten in mdoc(7) format making it readable by default with
mandoc, it also has been extended by OpenBSD to cover all awk(1) options

Obtained from: OpenBSD
MFH: 1 week