React DOM: Add support for hidden="until-found"

[eps1lon]

Summary

Closes #24740

Adds support for the experimental hidden="until-found" as well as the correspondig TODO onBeforeMatch event handler.

Keep in mind that these new browser APIs are only implemented in Chrome and Edge at the moment. Safari and Firefox have no support for this API yet (see hidden browser compatibility table.

I haven't checked if we can polyfill the API or maybe we shouldn't even do that? Otherwise landing this would take more time and block experimentation in UIs targetting Chromium exclusively

How did you test this change?

• Attribute fixture (commited changes with non-experimental build since this is the build we were using before)
• Codesandbox from repro will contain matching behavior of DOM and React: https://codesandbox.io/s/lucid-benz-u2oksw

[eps1lon]

Similar issue as #24730: Should this be behind a flag?

[sizebot]

Comparing: 4cd788a...eb16b74

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	131.79 kB	131.79 kB	=	42.40 kB	42.40 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	137.06 kB	137.06 kB	=	44.00 kB	44.00 kB
facebook-www/ReactDOM-prod.classic.js	=	457.17 kB	457.17 kB	=	83.22 kB	83.22 kB
facebook-www/ReactDOM-prod.modern.js	=	442.41 kB	442.41 kB	=	80.94 kB	80.94 kB
facebook-www/ReactDOMForked-prod.classic.js	=	457.94 kB	457.94 kB	=	83.33 kB	83.33 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against eb16b74

[react-sizebot]

Comparing: 01ab35a...a7cc853

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	+0.06%	176.89 kB	176.99 kB	+0.03%	55.14 kB	55.15 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	+0.02%	179.00 kB	179.04 kB	+0.01%	55.80 kB	55.81 kB
facebook-www/ReactDOM-prod.classic.js	+0.03%	594.04 kB	594.22 kB	+0.01%	104.94 kB	104.95 kB
facebook-www/ReactDOM-prod.modern.js	+0.03%	577.33 kB	577.51 kB	=	101.96 kB	101.97 kB
test_utils/ReactAllWarnings.js	Deleted	66.40 kB	0.00 kB	Deleted	16.26 kB	0.00 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
test_utils/ReactAllWarnings.js	Deleted	66.40 kB	0.00 kB	Deleted	16.26 kB	0.00 kB

Generated by 🚫 dangerJS against a7cc853

[eps1lon]

We'll also need to look into support for beforematch events and we need to decide if we're ok with experimental APIs that are only supported by a single browser.

[github-actions]

This pull request has been automatically marked as stale. If this pull request is still relevant, please leave any comment (for example, "bump"), and we'll keep it open. We are sorry that we haven't been able to prioritize reviewing it yet. Your contribution is very much appreciated.

[github-actions]

This pull request has been automatically marked as stale. If this pull request is still relevant, please leave any comment (for example, "bump"), and we'll keep it open. We are sorry that we haven't been able to prioritize reviewing it yet. Your contribution is very much appreciated.

[github-actions]

Closing this pull request after a prolonged period of inactivity. If this issue is still present in the latest release, please ask for this pull request to be reopened. Thank you!