dillon1000/react

Enable hooks in www build (#14116)

The `enableHooks` feature flag used to only control whether the API
was exposed on the React package. But now it also determines if the
dispatcher and implementation are included in the bundle.

We're using hooks in www, so I've switched the feature flag to `true`
in the www build.

(Alternatively, we could have two feature flags: one for the
implementation and dispatcher, and one for exposing the API on the
React package.)