dillon1000/react

Export captureOwnerStacks() only in DEV "react" builds (#29923)

Only with the enableOwnerStacks flag (which is not on in www).

This is a new DEV-only API to be able to implement what we do for
console.error in user space.

This API does not actually include the current stack that you'd get from
`new Error().stack`. That you'd have to add yourself.

This adds the ability to have conditional development exports because we
plan on eventually having separate ESM builds that use the "development"
or "production" export conditions.

NOTE: This removes the export of `act` from `react` in prod (as opposed
to a function that throws) - inline with what we do with other
conditional exports.