[DataGrid] Experiment with sticky column headers

[cherniavskii]

• I have followed (at least) the PR section of the contributing guide.

This is a sticky column headers idea borrowed from #9171 and applied to our current virtualization engine.

Demo: https://deploy-preview-9589--material-ui-x.netlify.app/x/react-data-grid/virtualization/#column-virtualization

[romgrk]

I'll probably pick this up soon.

Do you think we can implement all of this without breaking changes?

And do you think we should implement the fake scrollbars now? They bring some complexity, but the design change (scrollbar going up to the headers) is not going to be liked by everyone.

[cherniavskii]

Do you think we can implement all of this without breaking changes?

Probably not, but we could try to change as little as possible.
Also, the "breaking change" definition in this case is a bit blurry depending on whether we treat DOM structure as a public API - I can imagine that we do some structural DOM changes and release them in a minor version if they are not too drastic 🙂

And do you think we should implement the fake scrollbars now? They bring some complexity, but the design change (scrollbar going up to the headers) is not going to be liked by everyone.

Apart from complexity, are there any other drawbacks?

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