Bindings for Build API

[keller-mark]

It is unclear if this is needed. It might be better to encourage a short JSX single-file / string, such that anything more complicated would need to be published as a standalone NPM package with a thin wrapper. On the other hand, this could result in developers who are constrained to a single-file / string which becomes very long over time and cannot be easily split up. With many files, you would want things like HMR which might be better to delegate to a regular Node / Vite setup anyway. On the other hand, maybe file watching and running Build in response could be done entirely via Python without the Node/Vite setup