documentation/pdf: Improve zh-cn|zh-tw font issues
The build script now uses fonts installed by the port/pkg
docproj-fonts-cjk.
Differential Revision: https://reviews.freebsd.org/D36623
Differential Revision: https://reviews.freebsd.org/D37447
Co-authored-by: Danilo G. Baio <dbaio@FreeBSD.org>