Local paths in common voice
Continuation of https://github.com/huggingface/datasets/pull/3664:

- pass the `streaming` parameter to _split_generator
- update @anton-l's code to use this parameter for `common_voice`
- add a comment to explain why we use `download_and_extract` in non-streaming and `iter_archive` in streaming

Now the `common_voice` dataset has a local path back in `ds["path"]`, and this field is `None` in streaming mode.

cc @patrickvonplaten @anton-l @albertvillanova 

Fix #3663.