change udpos features structure

[cosmeowpawlitan]

The structure is change such that each example is a sentence
The change is done for issues:
#2061
#2444

Close #2061 , close #2444.

[lhoestq]

Thanks for updating the udpos features !

I also fixed the code formatting and regenerated the dataset_infos.json
This looks all good to me :)

To fix the CI we would need to add the yaml tags at the top of the /datasets/xtreme/README.md. Would you be interested in giving it a try ? Otherwise someone can probably add the tags later in another PR

[lhoestq]

Let's add the tags in another PR. Thanks again !

[albertvillanova]

Close #2061 , close #2444.