[Here is a video preview](https://up1.xwikisas.com/#xF5g0nTr9mZzyaNn9qvCGw) of the changes introduced in https://github.com/xwiki/xwiki-platform/pull/2475/commits/868e29f9fd1d4660c3f9b1c54bfa83d19bf52962
Now the resize handle is a small bar at the end of each column.