ncurses: Move termcap and tabset to ncurses-lib

termcap and tabset are currently in runtime, but since ncurses is the
only thing which uses them, they belong in the ncurses package.

curses without termcap is not very useful, so put them in the -lib
subpackage rather than ncurses itself, so that installing ncurses-lib
provides a working curses.

This change moves files between packages so, until we have a proper
policy on how to handle this in release/stable branches, it should
not be MFC'd.

MFC after: never
Discussed with: kevans
Reviewed by: manu, kevans
Sponsored by: https://www.patreon.com/bsdivy
Differential Revision: https://reviews.freebsd.org/D53610