x11/libinput: Update to 1.21.0

Release notes for 1.20: https://lists.x.org/archives/wayland-devel/2022-February/042111.html
Release notes for 1.21: https://gitlab.freedesktop.org/libinput/libinput/-/releases/1.21.0

Differential Revision: https://reviews.freebsd.org/D36917
Sponsored by: Beckhoff Automation GmbH & Co. KG