[core] Remove useIsFocusVisible util

[DiegoAndai]

Part of #40958
Closes: #14420

As :focus-visible is now supported in all our supported browsers (reference), we can remove this utility and rely completely on :focus-visible.

This is an intermediate step: ideally, we would use the :focus-visible pseudo-selector directly, but that would mean removing the focusVisible classes and refactoring many components.

[mui-bot]

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https://deploy-preview-42467--material-ui.netlify.app/

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and 38 more changes

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[mnajdova]

Just a precaution, have you tested that all these components behave identically once moving to use the :focus-visible pseudo selector in the oldest browsers we support? Just to make sure there won't introduce some subtle breaking changes with this.

[DiegoAndai]

Just a precaution, have you tested that all these components behave identically once moving to use the :focus-visible pseudo selector in the oldest browsers we support? Just to make sure there won't introduce some subtle breaking changes with this.

I tested all browsers, both minimally supported and latest versions. The only thing "not working" is the Link's focus visible in Firefox 115, but that's not working on master (mui.com) either. I think it might be a configuration issue. It's working correctly on the latest Firefox version (127). So, in summary, this is working the same way as master in all supported browsers. This makes sense as we were already relying in :focus-visible on all browsers in which it was available (reference).

This is ready for review 😊

[aarongarciah]

Very nice! Left some small comments and questions.

[aarongarciah]

yay!

[oliviertassinari]

I would have expected this to come from Base UI.

?

Suggested change

	export default function isFocusVisible(element: Element): boolean {
	// TODO import from Base UI
	export default function isFocusVisible(element: Element): boolean {

[DiegoAndai]

As mentioned in the description: "ideally, we would use the :focus-visible pseudo-selector directly, but that would mean removing the focusVisible classes and refactoring many components."

The isFocusVisible function is an intermediary step, so I don't think we should implement it in Base UI. When we reimplement the look of the library, we should use :focus-visible directly, deprecate the focusVisible classes, and eventually remove this function.