Build `react-dom` in `builds/facebook-fbsource` (#30711)

## Summary

Builds `react-dom` for React Native so that it also populates the
`builds/facebook-fbsource` branch.

**NOTE:** For Meta employees, D61354219 is the internal integration.

## How did you test this change?

```
$ yarn build
…
$ ls build/facebook-react-native/react-dom/cjs
ReactDOM-dev.js       ReactDOM-prod.js      ReactDOM-profiling.js
```