Reduce risk of leaving shipped Hooks as nullable on Dispatcher

[eps1lon]

By grepping for the feature flag you're now directed to the Dispatcher type. Members are only nullable if they're behind a feature flag so we should make them non-nullable when the flag ships. There's still the possibility that types are not updated when the flag is on everywhere but cleanup should flush it out.

[eps1lon]

This is available everywhere else.

[react-sizebot]

Comparing: f0edf41...d12a451

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	=	514.24 kB	514.24 kB	=	91.73 kB	91.73 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	=	556.18 kB	556.18 kB	=	98.72 kB	98.72 kB
facebook-www/ReactDOM-prod.classic.js	=	595.79 kB	595.79 kB	=	104.85 kB	104.85 kB
facebook-www/ReactDOM-prod.modern.js	=	586.21 kB	586.21 kB	=	103.30 kB	103.30 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against 858c71f

[sebmarkbage]

It really shouldn't be added everywhere since it's not an exposed API there's no reason to ship the bytes. A lot of the Cache stuff isn't gated properly.

[eps1lon]

It really shouldn't be added everywhere since it's not an exposed API there's no reason to ship the bytes. A lot of the Cache stuff isn't gated properly.

I think we just accidentally shipped this because it was part of enableCache which was removed in #31778.

Should we reintroduce a new flag that's only on for experimental (React Devtools needs it)? Though unstable_getCacheForType was also fully unflagged which is odd since it's still marked as unstable_.