packages: Install development manpages in the -dev package

Add a new per-group SUBPACKAGE option to bsd.man.mk. When MANSPLITPKG
is enabled, this is forced to "-man", otherwise it defaults to empty
but can be overridden by the caller.

Use this in bsd.lib.mk to install library manpages in the -dev package
instead of the base package. This is nearly always preferable, since
library manpages are usually in section 2 or 3 and are only relevant
to people with development packages installed.

For manpages which should be installed in the base package even for
libraries, add a new MANNODEV group in bsd.lib.mk. Update existing
Makefiles to use this where appropriate.

MFC after: 3 days
Discussed with: olce
Reviewed by: olce
Sponsored by: https://www.patreon.com/bsdivy
Differential Revision: https://reviews.freebsd.org/D52832