Better shards shuffling in streaming mode
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Sometimes a dataset script has a `_split_generators` that returns several files as well as the corresponding metadata of each file. It often happens that they end up in two separate lists in the `gen_kwargs`:
```python
gen_kwargs = {
    "files": [os.path.join(data_dir, filename) for filename in all_files],
    "metadata_files": [all_metadata[filename] for filename in all_files],
}
```
It happened for Multilingual Spoken Words for example in #3666

However currently **the two lists are shuffled independently** when shuffling the shards in streaming mode. This leads to `_generate_examples` not having the right metadata for each file.

To prevent this issue I suggest that we always shuffle lists of the same length the exact same way to avoid such a big but silent issue.

cc @polinaeterna 
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