Add: slider dialog.
Imported to enable testing and to complete the geomman(8) utility.

Developed as part of the "Full Disk Administration Tool for FreeBSD"
project, Braulio Rivas (brauliorivas@), Google Summer of Code 2025.

Sponsored by:	Google LLC (GSoC 2025)

Merge commit '5a70558d32b9680c10ab579c7491652e0838cee4'

libbsddialog >= 0.3 has a built-in form implementation so delete
formw dependency.

Approved by:		bapt (share/mk maintainer)
Differential Revision:	https://reviews.freebsd.org/D42167

Improvements and changes to integrate bsddialog(1) with scripts in BASE.
Overview:

 * New options. --and-widget, --keep-tite, --calendar.
 * Change output format. Menus and --print-maxsize.
 * Redefine sizing. Fixed rows, cols and menurows became at the most.
 * Add DIAGNOSTICS. Error messages for bad arguments and options.
 * Add keys. Space for --menu, fast keys for --msgbox and --yesno.
 * Text. Change default text modification, add --cr-wrap.

See /usr/src/contrib/bsddialog/CHANGELOG '2022-09-24 Version 0.4'
for more detailed information.

Merge commit '9f24fda5a8e7ab8243e71473c7e2dc98b4877e64'

Fix dialogs building and updating fault with disabled shadow
(conf.shadow=false and implicitly bsddialog --no-shadow).

While here delete WARNS=2: all warnings were fixed in upstream and
imported in 0.2.

Approved by:		bapt (mentor)
Differential Revision:	https://reviews.freebsd.org/D34958

Add _XOPEN_SOURCE_EXTENDED to use curses' get_wch() and to avoid a
building error after next "bsddialog 0.2" import.

Approved by:		bapt (mentor)
Differential Revision:	https://reviews.freebsd.org/D34419