resize the window size instead of expand editor pane

[liangzh-404]

Currently , when we use Zen mode, the editor pane will fill the size of left/right sidebar, which may be too large. And when we try to make it smaller, we will get a super small sidebar if we turn off zen mode.
I think a more convinient way is to shrink the window size to editor pane when we go into Zen mode

[Maxymillion]

Thanks @liangzh-404, this was the way I intended it to work. But I can look if I can add an option in the future to add this functionality as well.