Turbopack: fix export-all-as with name collision (#81510)
`EcmascriptModulePartReference` is a pretty counterintuitive reference. The `part` declares which module should be synthesised on the other side. That doesn't have anything to do with which exports are actually being imported by reference.
This only triggered a bug when these exports here had the same name by coincidence
```js
// reexport.js
export * as Sub from './sub.js' // <--
// sub.js
export const Sub = 123 // <--
```
