[feat] Add TextVQA dataset
_The documentation is not available anymore as the PR was closed or merged._ Hey :) Have you had a chance to continue this PR ? Let me know if you have questions or if I can help Hey @lhoestq, let me wrap this up soon. I will resolve your comments in next push.
This would be the first classification-based vision-and-language dataset in the datasets library.

Currently, the dataset downloads everything you need beforehand. See the [paper](https://arxiv.org/abs/1904.08920) for more details.

Test Plan:
- Ran the full and the dummy data test locally