Fix plugins/qpa build with Qt 5.13
Summary:
Upstream moved screen maintenance functions from
QPlatformIntegration to QWSI.
BUG: 406056
See also: https://code.qt.io/cgit/qt/qtbase.git/commit/?h=5.13&id=01e1df90
Test Plan: Built fine with Qt 5.12.2 and Qt 5.13 stable branch.
Reviewers: KWin, zzag
Reviewed By: KWin, zzag
Subscribers: zzag, arojas, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D20239