add `desc` to `tqdm` in `Dataset.map()`
Once this is merged, let's update `transformers` examples to use this new code. As currently all those tqdm bars are who knows what they are....

https://github.com/huggingface/transformers/issues/11797 Sure @stas00! Once this is merged let's discuss what all changes can be done on `transformers` side @bhavitvyamalik, as it has been merged would you like to tackle https://github.com/huggingface/transformers/issues/11797?
 Definitely @stas00. From what I could gather, you guys want more meaningful `.map` calls for all examples [here](https://github.com/huggingface/transformers/tree/master/examples/pytorch)? That's exactly right, @bhavitvyamalik 

Perhaps the best approach is to do one example, see that other maintainers agree on it. and then replicate to other.
Fixes #2330. Please let me know if anything is also required in this 