devel/libkiwix13: New port for libkiwix 13

This port is assumed to be temporary, as the reason for its creation is
that kiwix-tools 3.7.0, the latest released version at time of this
writing, relies on libkiwix with major version 13, whereas
devel/libkiwix was updated too soon to 14.

An alternative would be to bump PORTEPOCH for libkiwix, but such bumps
are forever and should be reserved for changes in version numbering as
much as possible.

Suggested by: jrtc27, jrm
Reviewed by: jrm
Fixes: dafb538b3fd6 ("devel/libkiwix: Update to 14.0.0")
MFH: 2025Q1
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D48395