Move to new file: Moving an import statement may break code

**Code**

See `moveToNewFile_moveImport.ts`.

```ts
[|import { a, b } from "m";
a;|]
b;
```

**Expected behavior:**

The import of `b` is kept in the original file since it's still needed.

**Actual behavior:**

The import is wholly removed from the old file, and an *extra* import is added to the new file for `a` even though it already has that.
