Add task templates for tydiqa and xquad
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Just tested TydiQA and it works fine :)
2021-06-18T14:26:28Z
https://github.com/huggingface/datasets/pull/2518#issuecomment-864078730
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2021-06-18T14:26:28Z
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This PR adds question-answering templates to the remaining datasets that are linked to a model on the Hub.

Notes: 

* I could not test the tydiqa implementation since I don't have enough disk space 😢 . But I am confident the template works :)
* there exist other datasets like `fquad` and `mlqa` which are candidates for question-answering templates, but some work is needed to handle the ordering of nested column described in #2434 

