[core] Batch small changes

[oliviertassinari]

• [docs] Remove outdated notification 6d6c432: This is a sync with master, we were linking Adobe XD, which was released a good 6 months ago.
• [docs] Remove divjoy, it's not working c5b2d95. Not enough sales to justify the overhead.
• [docs] Fix 404 with license markdown 6ccda57. It's linked in https://unpkg.com/browse/@material-ui/x-grid@4.0.0-alpha.31/LICENSE.md. Related to [license] Move license content to a standalone page mui-x#1865
• [docs] Improve Scroll playground code output d90fd70: See the page on https://next.material-ui.com/components/popper/#scroll-playground
• [core] Clarify why we need this CSS property d2b4c45: I have recently realized that we will be able to remove this CSS property. https://developer.apple.com/documentation/safari-release-notes/safari-13-release-notes. This should help us remove the property in the future once we drop iOS 12 support.
• [core] Fix yarn benchmark:browser command a939e99. I have found that the command was broken when writing [Rating] Make input ids less predictable #26493 (comment).
• [Grid] List missing props 8bc21fb: a quick follow-up after [Grid] Add responsive direction and spacing props #26590

[mui-pr-bot]

No bundle size changes (experimental)

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