Click Tree view, scroll the selected item to the middle of the view

I noticed when tree view item is clicked, if the item is in the current view, there is no scroll. However, still need to scan the whole view to find the item.
I'd propose to scroll the selected item to middle of the view, unless it's already scrolled down to the bottom.

I guess the code is here: https://github.com/alibaba/structure-view/blob/41474513bd0bbca6c22e891779f0816becae4715/lib/util.js#L18

Open lib/util.js at the referenced line and trace the tree-item click handling. Reproduce clicking an item that is already visible, then verify it scrolls toward the middle of the view while leaving an item near the bottom from being scrolled past the bottom. Done means the selected item is easier to locate without changing the existing tree selection behavior.

Written by the indexing model from the issue text.