[docs] Update Accessibility to be more up to date

[oliviertassinari]

An opportunity was encountered at https://mui.zendesk.com/agent/tickets/7043.

Going forward, this introduction would be much better moved into a more general page. It's way more general than the data grid.

[mui-bot]

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📖	Netlify deploy preview: https://deploy-preview-7970--material-ui-x.netlify.app/

These are the results for the performance tests:

Test case	Unit	Min	Max	Median	Mean	σ
Filter 100k rows	ms	740.5	915.3	785.3	816.52	75.803
Sort 100k rows	ms	707.7	1,042	895.4	907.94	110.749
Select 100k rows	ms	198.8	310.6	244.9	256.22	43.263
Deselect 100k rows	ms	172.3	266.5	184.3	196.56	35.403

Generated by 🚫 dangerJS against 03f2b1e