解决MouseLeftButtonDown与Click事件冲突

MouseLeftButtonDown与Click事件同时存在时，系统默认直行click事件。想要MouseLeftButtonDown事件可用，解决方法如下：

this.AddHandler(InkCanvas.MouseLeftButtonDownEvent, new MouseButtonEventHandler(this.aa_MouseLeftButtonDown), true);

void aa_MouseLeftButtonDown(object sender, MouseButtonEventArgs e){}