[qtgui] Fix crash when a focused window's surface is destroyed. Contr…

…ibutes to JB#40880

Ensure full focus out and in are processed when transferring focus to the
parent window, otherwise the focusObjectChanged() signal of the window
whose window was destroyed will remain connected to
QGuiApplicationPrivate::_q_setFocusObject() and that can result in
an object not belonging to the active window (assuming there is one)
getting focus.

src/gui/kernel/qwindow.cpp

@@ -1651,7 +1651,7 @@ void QWindow::destroy()
     }
 
     if (QGuiApplicationPrivate::focus_window == this)
-        QGuiApplicationPrivate::focus_window = parent();
+        QWindowSystemInterface::handleWindowActivated(parent());
     if (QGuiApplicationPrivate::currentMouseWindow == this)
         QGuiApplicationPrivate::currentMouseWindow = parent();
     if (QGuiApplicationPrivate::currentMousePressWindow == this)