[Fiber] Support moveBefore at the top level of a container

[sebmarkbage]

Parity with appendChild and insertBefore. This allows reordering at the root while preserving state.

[react-sizebot]

Comparing: d2a1b88...d243516

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	=	1.83 kB	1.82 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	513.98 kB	513.98 kB	=	91.79 kB	91.79 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	548.08 kB	548.01 kB	=	97.52 kB	97.51 kB
facebook-www/ReactDOM-prod.classic.js	=	595.86 kB	595.86 kB	=	104.87 kB	104.87 kB
facebook-www/ReactDOM-prod.modern.js	=	586.29 kB	586.29 kB	=	103.32 kB	103.32 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
react-native/implementations/ReactFabric-prod.fb.js	+0.89%	379.36 kB	382.72 kB	+0.99%	65.85 kB	66.50 kB
react-native/implementations/ReactNativeRenderer-prod.fb.js	+0.87%	384.79 kB	388.16 kB	+1.00%	66.80 kB	67.47 kB
react-native/implementations/ReactFabric-profiling.fb.js	+0.83%	404.85 kB	408.21 kB	+0.95%	69.70 kB	70.36 kB
react-native/implementations/ReactNativeRenderer-profiling.fb.js	+0.82%	410.25 kB	413.62 kB	+0.91%	70.62 kB	71.26 kB

Generated by 🚫 dangerJS against dfbceb9

[Hardelzs]

This development is significant for web developers, as it offers a more efficient way to manage dynamic content updates without losing the current state of elements.