fix: dock wakeup area not changed

When dock is hidden, position change through DBus will not change
frontend rect, thus not update wakeup area. This is because position
in WindowManager is not changed. Emit positionChanged signal in
MultiScreenWorker.

Log: fix dock wakeup area not changed
Issue: https://github.com/linuxdeepin/developer-center/issues/5831

frame/util/multiscreenworker.cpp

@@ -181,6 +181,7 @@ void MultiScreenWorker::onPositionChanged(int position)
     qDebug() << "position change from: " << lastPos << " to: " << position;
 #endif
     m_position = static_cast<Position>(position);
+    Q_EMIT positionChanged(m_position);
 
     if (m_hideMode == HideMode::KeepHidden || (m_hideMode == HideMode::SmartHide && m_hideState == HideState::Hide)) {
         // 这种情况切换位置,任务栏不需要显示