Should IntegerArray provide data / mask through an API?
I'm currently implementing some algorithms on top of the `IntegerArray` class with `numba`. Therefore I would need to pass in the two separate backing NumPy arrays instead of the `pandas` class. Using `series.to_numpy()` isn't helpful in this case as this returns a `object`-typed array. For now, I'll keep using `series.values._data` and `series.values._mask` but I'm aware that using private variables is not a long-term solution.

Given that `series.values._data` may be undefined where the mask is `True`, I know that returning the raw `data` may be a bit controversial but still need. Thus naming the accessor for it should be done carefully.