Client: Call parent requestUpdate after changing subsurface position

Calling setPosition on a child window would not send the appropriate commit
request after the wl_subsurface.set_position request.

Task-number: QTBUG-52118
Change-Id: I792016ce7e0a5a2efd3a32a98727b43ee0275b0e
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>
Reviewed-by: Giulio Camuffo <giulio.camuffo@kdab.com>

src/client/qwaylandwindow.cpp

@@ -262,6 +262,7 @@ void QWaylandWindow::setGeometry_helper(const QRect &rect)
     if (mSubSurfaceWindow) {
         QMargins m = QPlatformWindow::parent()->frameMargins();
         mSubSurfaceWindow->set_position(rect.x() + m.left(), rect.y() + m.top());
+        mSubSurfaceWindow->parent()->window()->requestUpdate();
     } else if (shellSurface() && window()->transientParent() && window()->type() != Qt::Popup)
         shellSurface()->updateTransientParent(window()->transientParent());
 }
@@ -638,6 +639,8 @@ bool QWaylandWindow::createDecoration()
             QMargins m = frameMargins();
             subsurf->set_position(pos.x() + m.left(), pos.y() + m.top());
         }
+        if (!mChildren.isEmpty())
+            window()->requestUpdate();
     }
 
     return mWindowDecoration;