Add `features` param to `IterableDataset.map`
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_The documentation is not available anymore as the PR was closed or merged._
## Description

As suggested by @lhoestq in #3888, we should be adding the param `features` to `IterableDataset.map` so that the features can be preserved (not turned into `None` as that's the default behavior) whenever the user passes those as param, so as to be consistent with `Dataset.map`, as it provides the `features` param so that those are not inferred by default, but specified by the user, and later validated by `ArrowWriter`.

This is internally handled already by the functions relying on `IterableDataset.map` such as `rename_column`, `rename_columns`, and `remove_columns` as described in #5287.

## Usage Example

```python
from datasets import load_dataset, Features

ds = load_dataset("rotten_tomatoes", split="validation", streaming=True)
print(ds.info.features)
ds = ds.map(
    lambda x: {"target": x["label"]},
    features=Features(
        {"target": ds.info.features["label"], "label": ds.info.features["label"], "text": ds.info.features["text"]}
    ),
)
print(ds.info.features)
```
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