multimedia/libzen: Update to 0.4.40

• Use proper upstream version
• Switch to separate source archives
• Switch to CMake which brings us much closer to other distributions
• Sanitize source code

Reference: https://github.com/MediaArea/ZenLib

Changelog: https://github.com/MediaArea/ZenLib/releases/tag/v0.4.40

PR: 268707
Approved by: portmgr (maintainer timeout, 2+ weeks)