New port x11-wm/lxqt LXQt DE meta-port

LXQt is an advanced, easy-to-use, and fast desktop environment based on
Qt technologies. It has been tailored for users who value simplicity,
speed, and an intuitive interface. Unlike most desktop environments,
LXQt also works fine with less powerful machines.

PR: 229318
Approved by: miwi (mentor)
Differential Revision: https://reviews.freebsd.org/D19003