x11/libxkbcommon: Update to 1.13.1

While here, use PLIST_SUB instead of PLIST_FILES for conditional plist
entries according to selected options. [1]

Changelog: https://github.com/xkbcommon/libxkbcommon/blob/xkbcommon-1.13.1/NEWS.md

PR: 291943
Suggested by: arrowd (via ports-committers) [1]
Approved by: manu (x11)