[dev-tool] react to typing changes in rollup v2.78 (Azure#23059)

* [dev-tool] react to typing changes in rollup v2.78

Previously the type for `load` is `any`. Now it can also be a object

```
type ObjectHook<T, O = {}> = T | ({ handler: T; order?: 'pre' | 'post' | null } & O);
```

This PR adds type narrowing to fix TypeScript build error.

* bump rollup version

Author: jeremymeng