[data grid] position: absolute for rows to avoid repaint

[oliviertassinari]

Summary

This is a follow-up on #11866 (comment). See point 3 there. There seems to be a simple opportunity to increase performance by about 5% (30ms out of 700ms).

Today the virtualization layout looks like this:

So each time we add or remove a row at the top of the list, we have to repaint.

Instead, we could use position: absolute (while keeping the transform)

Motivation

Performance. Now, it seems to be only a hard 5% win, so not a priority.

The main win might be more about the green repaint flash that could feel like a red flag 🚩 by developers that stays on the surface of things, so more of a marketing value.

Screen.Recording.2024-02-26.at.02.27.30.mov

I think something to prioritize only when we seek quick wins or when someone complains about performance.

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[romgrk]

@cherniavskii Pointed out in #12023 that position: absolute makes dynamic 'auto' row height UX less smooth, because we need one render before knowing the real position where to place rows.