Use default cast for sliced list arrays if pyarrow >= 4
I believe we don't use PyArrow >= 4.0.0 because of some segfault issues:
https://github.com/huggingface/datasets/blob/1206ffbcd42dda415f6bfb3d5040708f50413c93/setup.py#L78
Can you confirm @lhoestq ? @SBrandeis pyarrow version 4.0.1 has fixed that issue: #2489 😉 
From pyarrow version 4, it is supported to cast sliced lists.

This PR uses default pyarrow cast in Datasets to cast sliced list arrays if pyarrow version is >= 4.

In relation with PR #2461 and #2490.

cc: @lhoestq, @abhi1thakur, @SBrandeis