[core] Small changes

[oliviertassinari]

• [core] import * as React from 'react' a1d5aeb: Noticed a few cases that diverge from the convention
• [core] Resolve hesitation between @return vs. @returns 7913d02: the two are aliases, I went with @returns because more popular (in the codebase).
• [core] Remove blank line for consistency 8d0d352: follow the convention
• [test] Fix test:coverage:html 7b3faab: the command got out of date
• [core] Sort gitignore ASC e1e52df: so we don't have to ask ourselves, where should I put the new value.
• [docs] Simpler > easier c851384: simple: one bread, easy: no effort. Isn't simplicity a better property to aim for than easiness?
• [docs] v5 in Q3 is unrealistic 2f135bd
• [core] Point to next over master c4fcc2a:
• [docs] We don't allow the .jsx extension 4b15574:
• [job] Add levels 07d64fb:
• [docs] Skip anchor link for h1 9b980c7: the anchor on the h1 duplicates with the naked URL, it's noise. I found it with Algolia that always returns an anchor even when it matches the top of the page. reactjs.org does the same, docusaurus.io and many others too.
• [test] Improve lint commands 3e1442b: a small detail we changed in the x repository so we could add a CSS lint stage.

[mui-pr-bot]

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