[flow] Add web host element libdefs

[jbrown215]

No description provided.

[react-sizebot]

Comparing: 1bd1f01...820700d

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.js	=	6.68 kB	6.68 kB	+0.11%	1.83 kB	1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	536.16 kB	536.16 kB	=	94.80 kB	94.80 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	+0.11%	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	663.75 kB	663.75 kB	=	117.02 kB	117.02 kB
facebook-www/ReactDOM-prod.classic.js	=	687.70 kB	687.70 kB	=	121.07 kB	121.07 kB
facebook-www/ReactDOM-prod.modern.js	=	678.12 kB	678.12 kB	=	119.43 kB	119.43 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against 820700d