dataset.to_iterable_dataset() loses useful info like dataset features
{'login': 'Hubert-Bonisseur', 'id': 48770768, 'node_id': 'MDQ6VXNlcjQ4NzcwNzY4', 'avatar_url': 'https://avatars.githubusercontent.com/u/48770768?v=4', 'gravatar_id': '', 'url': 'https://api.github.com/users/Hubert-Bonisseur', 'html_url': 'https://github.com/Hubert-Bonisseur', 'followers_url': 'https://api.github.com/users/Hubert-Bonisseur/followers', 'following_url': 'https://api.github.com/users/Hubert-Bonisseur/following{/other_user}', 'gists_url': 'https://api.github.com/users/Hubert-Bonisseur/gists{/gist_id}', 'starred_url': 'https://api.github.com/users/Hubert-Bonisseur/starred{/owner}{/repo}', 'subscriptions_url': 'https://api.github.com/users/Hubert-Bonisseur/subscriptions', 'organizations_url': 'https://api.github.com/users/Hubert-Bonisseur/orgs', 'repos_url': 'https://api.github.com/users/Hubert-Bonisseur/repos', 'events_url': 'https://api.github.com/users/Hubert-Bonisseur/events{/privacy}', 'received_events_url': 'https://api.github.com/users/Hubert-Bonisseur/received_events', 'type': 'User', 'site_admin': False}
[{'id': 1935892871, 'node_id': 'MDU6TGFiZWwxOTM1ODkyODcx', 'url': 'https://api.github.com/repos/huggingface/datasets/labels/enhancement', 'name': 'enhancement', 'color': 'a2eeef', 'default': True, 'description': 'New feature or request'}, {'id': 1935892877, 'node_id': 'MDU6TGFiZWwxOTM1ODkyODc3', 'url': 'https://api.github.com/repos/huggingface/datasets/labels/good%20first%20issue', 'name': 'good first issue', 'color': '7057ff', 'default': True, 'description': 'Good for newcomers'}]
{'login': 'Hubert-Bonisseur', 'id': 48770768, 'node_id': 'MDQ6VXNlcjQ4NzcwNzY4', 'avatar_url': 'https://avatars.githubusercontent.com/u/48770768?v=4', 'gravatar_id': '', 'url': 'https://api.github.com/users/Hubert-Bonisseur', 'html_url': 'https://github.com/Hubert-Bonisseur', 'followers_url': 'https://api.github.com/users/Hubert-Bonisseur/followers', 'following_url': 'https://api.github.com/users/Hubert-Bonisseur/following{/other_user}', 'gists_url': 'https://api.github.com/users/Hubert-Bonisseur/gists{/gist_id}', 'starred_url': 'https://api.github.com/users/Hubert-Bonisseur/starred{/owner}{/repo}', 'subscriptions_url': 'https://api.github.com/users/Hubert-Bonisseur/subscriptions', 'organizations_url': 'https://api.github.com/users/Hubert-Bonisseur/orgs', 'repos_url': 'https://api.github.com/users/Hubert-Bonisseur/repos', 'events_url': 'https://api.github.com/users/Hubert-Bonisseur/events{/privacy}', 'received_events_url': 'https://api.github.com/users/Hubert-Bonisseur/received_events', 'type': 'User', 'site_admin': False}
[{'login': 'Hubert-Bonisseur', 'id': 48770768, 'node_id': 'MDQ6VXNlcjQ4NzcwNzY4', 'avatar_url': 'https://avatars.githubusercontent.com/u/48770768?v=4', 'gravatar_id': '', 'url': 'https://api.github.com/users/Hubert-Bonisseur', 'html_url': 'https://github.com/Hubert-Bonisseur', 'followers_url': 'https://api.github.com/users/Hubert-Bonisseur/followers', 'following_url': 'https://api.github.com/users/Hubert-Bonisseur/following{/other_user}', 'gists_url': 'https://api.github.com/users/Hubert-Bonisseur/gists{/gist_id}', 'starred_url': 'https://api.github.com/users/Hubert-Bonisseur/starred{/owner}{/repo}', 'subscriptions_url': 'https://api.github.com/users/Hubert-Bonisseur/subscriptions', 'organizations_url': 'https://api.github.com/users/Hubert-Bonisseur/orgs', 'repos_url': 'https://api.github.com/users/Hubert-Bonisseur/repos', 'events_url': 'https://api.github.com/users/Hubert-Bonisseur/events{/privacy}', 'received_events_url': 'https://api.github.com/users/Hubert-Bonisseur/received_events', 'type': 'User', 'site_admin': False}]
Hi ! Oh good catch. I think the features should be passed to `IterableDataset.from_generator()` in `to_iterable_dataset()` indeed.

Setting this as a good first issue if someone would like to contribute, otherwise we can take care of it :) #self-assign seems like the feature parameter is missing from `return IterableDataset.from_generator(Dataset._iter_shards, gen_kwargs={"shards": shards})`  hence it defaults to None.
### Describe the bug

Hello,
I like the new `to_iterable_dataset` feature but I noticed something that seems to be missing.

When using `to_iterable_dataset` to transform your map style dataset into iterable dataset, you lose valuable metadata like the features. 

These metadata are useful if you want to interleave iterable datasets, cast columns etc.

### Steps to reproduce the bug

```python
dataset = load_dataset("lhoestq/demo1")["train"]
print(dataset.features)
# {'id': Value(dtype='string', id=None), 'package_name': Value(dtype='string', id=None), 'review': Value(dtype='string', id=None), 'date': Value(dtype='string', id=None), 'star': Value(dtype='int64', id=None), 'version_id': Value(dtype='int64', id=None)}
dataset = dataset.to_iterable_dataset()
print(dataset.features)
# None
```

### Expected behavior

Keep the relevant information

### Environment info

datasets==2.10.0
{'url': 'https://api.github.com/repos/huggingface/datasets/issues/5568/reactions', 'total_count': 0, '+1': 0, '-1': 0, 'laugh': 0, 'hooray': 0, 'confused': 0, 'heart': 0, 'rocket': 0, 'eyes': 0}