Changelog for 18.1

[gaearon]

Assumes #24404 is merged.
Needs a date in the header before merge.

[sizebot]

Comparing: 3547729...22f6d9f

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	=	131.52 kB	131.52 kB	=	42.10 kB	42.10 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	136.79 kB	136.79 kB	=	43.68 kB	43.67 kB
facebook-www/ReactDOM-prod.classic.js	=	441.27 kB	441.27 kB	=	80.48 kB	80.48 kB
facebook-www/ReactDOM-prod.modern.js	=	426.52 kB	426.52 kB	=	78.30 kB	78.30 kB
facebook-www/ReactDOMForked-prod.classic.js	=	441.27 kB	441.27 kB	=	80.48 kB	80.48 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

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