Enable Fast Filtering using Arrow Dataset

Hi @lhoestq,

As mentioned in Issue #1796, I would love to work on enabling fast filtering/mapping. Can you please share the expectations? It would be great if you could point me to the relevant methods/files involved. Or the docs or maybe an overview of `arrow_dataset.py`. I only ask this because I am having trouble getting started ;-;

Any help would be appreciated.

Thanks,
Gunjan