x11/libxkbcommon: Update to 1.8.0

Switch to github as tarball are not distributed anymore on the website.
While here, sort pkg-plist.

Release notes: https://lists.freedesktop.org/archives/wayland-devel/2025-February/043969.html

Differential Revision: https://reviews.freebsd.org/D49341
Sponsored by: Beckhoff Automation GmbH & Co. KG