[platforms/virtual] Support setting random screen geometries

A signal is added to the VirtualBackend to change all screen geometries.
This can be used from auto tests to change the screens. But it's not yet
correctly reflected in other areas. E.g. not forwarded to Wayland Output,
etc.

plugins/platforms/virtual/screens_virtual.cpp

@@ -36,6 +36,13 @@ void VirtualScreens::init()
     KWin::Screens::init();
     connect(m_backend, &VirtualBackend::sizeChanged,
             this, &VirtualScreens::startChangedTimer);
+    connect(m_backend, &VirtualBackend::outputGeometriesChanged, this,
+        [this] (const QVector<QRect> &geometries) {
+            // TODO: update Wayland Output
+            m_geometries = geometries;
+            emit changed();
+        }
+    );
     updateCount();
     emit changed();
 }

plugins/platforms/virtual/virtual_backend.h

@@ -64,6 +64,7 @@ public:
 
 Q_SIGNALS:
     void sizeChanged();
+    void outputGeometriesChanged(const QVector<QRect> &geometries);
 
 private:
     QSize m_size;