BUG: EAs with list-like values fail in to_csv (due to to_native_types)
From a report at GeoPandas: https://github.com/geopandas/geopandas/issues/1145

Explanation: assume you have an ExtensionArray with list-like values (eg with an object numpy array with lists under the hood). When calling, `to_csv`, which goes through `Block.to_native_types`, we convert this to a numpy array and call `astype(str)`:

https://github.com/pandas-dev/pandas/blob/39602e7d7c5b663696f5a6eca9e66e65483bc868/pandas/core/internals/blocks.py#L699

But, in numpy, if you have a numpy array with list like values, doing `astype(str)` does not work:

```
In [2]: a = np.array([[1, 2], [3]], dtype=object) 

In [3]: a.astype(str)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-3-db38302b5f9a> in <module>
----> 1 a.astype(str)

ValueError: setting an array element with a sequence
```

This could be considered a numpy issue, but, we should also avoid converting to a numpy array while we can directly call `astype` on the ExtensionArray.