[barrel] Use modern namespace re-export

```ts
// codegen:start {preset: barrel, include: ./sources/index.ts, import: star }
import * as sources from './sources/index'

export { sources }
// codegen:end
```

Could be:

```ts
// codegen:start {preset: barrel, include: ./sources/index.ts, import: star }
export * as sources from './sources/index'
// codegen:end
```