Improve performance when scrolling or resizing

[mc-petry]

Improve performance when:

• scrolling or resizing horizontal in vertical list (and reverse case).

How:

• save previous state and compare with new one

Example why:

Suppose we have huge table with vertical virtualization only. Inside table exist horizontal scroll without virtualization. And we have collapsible sidebar with nice animation. Currently on horizontal resize and scroll change virtualizer recalculates everything that dramatically reduce performance in fact of ugly animation.

[mc-petry]

PR #335