Move to new file doesn't maintain prologues directives, ts-check

```js
// @ts-check
"use strict";

export function foo() {
    return bar();
}

function bar() {
    return 100;
}
```

Use a refactoring to move `bar` to a new file.

**Expected**

```js
// @ts-check
"use strict";

export function bar() {
    return 100;
}
```

**Actual**

```js
export function bar() {
    return 100;
}
```