Improve scrolling/centering of nodes as you browse trees

[bvaughn]

Fix horizontal offset when nodes are selected. Selecting a node will scroll vertically devtools to ensure it's visible but not horizontally. Deep trees can be confusing in this way.

Clicking on a node in devtools that's near the boundary shouldn't jump the frame either. Only jump when an element is clicked outside.

The custom scroll to method is nice in that it maintains some padding around the top/bottom as we're scrolling, but...we can improve it?

[bvaughn]

React DevTools has been rewritten and recently launched a new version 4 UI. The source code for this rewrite was done in a separate repository and now lives in the main React repo (github.com/facebook/react).

Because version 4 was a total rewrite, and all issues in this repository are related to the old version 3 of the extension, I am closing all issues in this repository. If you can still reproduce this issue, or believe this feature request is still relevant, please open a new issue in the React repo: https://github.com/facebook/react/issues/new?labels=Component:%20Developer%20Tools