Improve appearance of the logout dialog on wayland

Summary:
The logout dialog has a taskbar entry and appears like a regular window on
wayland. This is because Qt does not support fullscreen windows with xdg_shell
as of 5.9.4. wl-shell works, so force it for the time being.

Test Plan: Ran ksmserver-logout-greeter on X11 and wayland, looks identical now.

Reviewers: #plasma, graesslin, davidedmundson, bshah

Reviewed By: #plasma, graesslin, bshah

Subscribers: ngraham, bshah, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D10425

ksmserver/logout-greeter/main.cpp

@@ -163,6 +163,9 @@ bool Greeter::eventFilter(QObject *watched, QEvent *event)
 
 int main(int argc, char *argv[])
 {
+    // Qt does not currently (5.9.4) support fullscreen on xdg_shell v6.
+    qputenv("QT_WAYLAND_SHELL_INTEGRATION", "wl-shell");
+
     QQuickWindow::setDefaultAlphaBuffer(true);
     QApplication app(argc, argv);
 

ksmserver/switchuser-greeter/main.cpp

@@ -135,6 +135,9 @@ bool Greeter::eventFilter(QObject *watched, QEvent *event)
 
 int main(int argc, char *argv[])
 {
+    // Qt does not currently (5.9.4) support fullscreen on xdg_shell v6.
+    qputenv("QT_WAYLAND_SHELL_INTEGRATION", "wl-shell");
+
     QQuickWindow::setDefaultAlphaBuffer(true);
     QGuiApplication app(argc, argv);