Remove $FreeBSD$: one-line .h pattern

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

Fix multiple warnings in usr.bin/top about discarded qualifiers from
both clang and gcc, by either constifying variables, or when that is not
possible, using __DECONST.

MFC after: 1 week

top(1): forgot in r336160

Approved by: gnn (mentor)
Differential Revision: https://reviews.freebsd.org/D16452

top(1) - support UTF-8 display

Reviewed by: eadler
Approved by: gnn (mentor)
Differential Revision: https://reviews.freebsd.org/D16006

top(1): format_time, format_k, etc.

- Use humanize_number for format_k and format_k2
- Fix some style nits in format_time

top(1): style and related

- style(9)
- remove now-defunct comments
- remove getuid check for low delay
- expand range of format_k

top(1): Use strsep instead of homegrown alternative

This replaces some complex, and not quite correct logic, with a more
common strsep pattern.

Reviewed by: mmacy (older version)

top(1): another pass of cleanup

- avoid the need to call a function to get size of known array. I'll
likely re-arrange some of the indirect in a later to avoid the magic
constants.
- use correct type
- add const
- replace caddr_t with void*. This corrects an alignment warning.
- remove duplicated include from immediately prior commit

Under base clang we're now down to:
- 3 warning in top.c, 1 warning in mahcine.c, 4 warning in display.c,
- 1 warning in utils.c

Tested with base clang, gcc7, gcc9, base gcc (mips)

top(1): partial revert of r334517

In fixing issues with uid > INT_MAX, I broke the uid without username
case. The latter is more important so return the old state.

Discussed with: allanjude

top: add -p option and p command to only show a single process

Allow to show only a single process specified by PID. This could
be done either by running top like 'top -p PID' or using the 'p' command
inside top.

Reviewed by: eadler
Approved by: eadler
Obtained from: OpenBSD
Differential Revision: https://reviews.freebsd.org/D15501

Use stpcpy instead of home grown solution

top(1): const poison

top(1) has a number of issues with writing to const strings. Begin
helping this along by marking easy cases as const.

top(1): Use uid_t for uid rather than 'int'

Remove unneeded define while here.

top(1): Quiesce several warnings

This is all warnings at level six (6) that are not
char-subscripts, incompatible-pointer-types,
sign-compare, switch, int-conversion,
missing-variable-declarations, cast-qual, cast-align

Some warnings that are fixed by this commit are:
shadow, strict-prototypes, missing-prototypes, pointer-arith,
unused-parameter, unused-const-variable, and several others

top(1): Migrate top to usr.bin

We've been maintaining top(1) for a long time, and the upstream
hasn't existed/been used in similarly as long. Make it clear that we own
top(1)

Tested with 'make universe'. Everything passed except MIPS which failed
for unrelated reasons. Install also tested for amd64.

Reviewed by: sbruno
No objections: imp, mmacy
Differential Revision: https://reviews.freebsd.org/D15387