Summary: Added SAL_USE_VCLPLUGIN=qt5 enviroment variable in session.conf xdg so libreoffice use qt5 vcl plugin See T146 for context. Test Plan: run env in terminal and se the value of SAL_USE_VCLPLUGIN Reviewers: wxl, tsimonq2, kc2bez Reviewed By: wxl, kc2bez Subscribers: wxl Differential Revision: https://phab.lubuntu.me/D72