Remove or add window decorations when toggling fullscreen

Task-number: QTBUG-55343
Change-Id: I38e94a70585ba93d40de22698fda80530cf2156d
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

src/client/qwaylandwindow.cpp

@@ -823,6 +823,7 @@ bool QWaylandWindow::setWindowStateInternal(Qt::WindowState state)
     mState = state;
 
     if (mShellSurface) {
+        createDecoration();
         switch (state) {
             case Qt::WindowFullScreen:
                 mShellSurface->setFullscreen();