Port away from deprecated methods in Qt 5.14
Test Plan: Builds with -DQT_DISABLE_DEPRECATED_BEFORE=0x060000 (as of today)
Reviewers: davidedmundson, broulik, apol
Reviewed By: apol
Subscribers: kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D23970