Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r235357,r235358,r235371,r235373,r235376:

Fix various mdoc(7) style nits.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Add an option to have a fail point term only execute when run by a
specified pid. This is helpful for automated testing involving a global
knob that would otherwise be executed by many other threads.

MFC after: 1 week

mdoc: drop redundant .Pp and .LP calls

They have no effect when coming in pairs, or before .Bl/.Bd

mdoc: move CAVEATS, BUGS and SECURITY CONSIDERATIONS sections to the
bottom of the manpages and order them consistently.

GNU groff doesn't care about the ordering, and doesn't even mention
CAVEATS and SECURITY CONSIDERATIONS as common sections and where to put
them.

Found by: mdocml lint run
Reviewed by: ru

Fix several typos in macros or macro misusage.

Found by: make manlint
Reviewed by: ru
Approved by: philip (mentor)

Fix mdoc, typos, contractions.

This includes:
PR: 135520
Submitted by: Nobuyuki Koganemaru
Patch by: gavin
MFC after: 3 days

Fix style/grammar issues in fail(9) man page.

Suggested by: Ben Kaduk
Approved by: dfr (mentor)

fail(9) support:

Add support for kernel fault injection using KFAIL_POINT_* macros and
fail_point_* infrastructure. Add example fail point in vfs_bio.c to
simulate VM buf pressure.

Approved by: dfr (mentor)