clang-format: [JS] support import/export type

Contributed by @jankuehle!

Users can choose to only import/export the type of the symbol (not value nor namespace) by adding a `type` keyword, e.g.:

```
import type {x} from 'y';
import {type x} from 'y';
export type {x};
export {type x};
```

Previously, this was not handled and would:
- Terminate import sorting
- Remove the space before the curly bracket in `export type {`

With this change, both formatting and import sorting work as expected.

Reviewed By: MyDeveloperDay, krasimir

Differential Revision: https://reviews.llvm.org/D150116