Inject the runtime to a global instead of exposing internals

See https://github.com/facebook/react-devtools/commit/673de20a4a0654ab849575307b9cf87fde53439e

This allows us to hide the internals in a better way.

It also allows us to detect React regardless of module system and it's a cheap way to detect React loading after page load.

This breaks dependencies on `__internals` as they would be anyway, anytime we change any internals.