share/termcap: add xterm-ghostty entry

As generated by ghostty during the build with some copy-editing.

Submitted by: Tim Culverhouse <tim@timculverhouse.com>
PR: 287642
Event: Berlin Hackathon 202507
MFC after: 1 week

(cherry picked from commit 804f961c5cddcffa950ff7f13025021cdd95ba46)