GridSplitter 可拖动
左右拖动
<GridSplitter Width="3" VerticalAlignment="Stretch" HorizontalAlignment="Center" ShowsPreview="False"/>
上下拖动
<GridSplitter Height="3" VerticalAlignment="Center" HorizontalAlignment="Stretch" ShowsPreview="False"/>
<GridSplitter Width="3" VerticalAlignment="Stretch" HorizontalAlignment="Center" ShowsPreview="False"/>
<GridSplitter Height="3" VerticalAlignment="Center" HorizontalAlignment="Stretch" ShowsPreview="False"/>