JS should allow merging/expando properties on imports

```js
// Filename: mod.js
export const Ns = function () { }

// @Filename: use.js
import { Ns } from './mod'
Ns.expando = 1
```

**Expected behavior:**
No error, and Ns has property 'expando'

**Actual behavior:**
Error, 'expando' not found on 'Ns'.

This merge shouldn't be allowed in Typescript, but it will work in Javascript, so it should be allowed there.