API: expected result for pow(1, pd.NA) or pow(pd.NA, 0)
Should `pow(1, pd.NA)` be `1` or `NA`?

```python
In [1]: import pandas as pd

In [2]: 1 ** pd.NA
Out[2]: NA

In [3]: import numpy as np

In [5]: 1 ** np.nan
Out[5]: 1.0
```

cc @jorisvandenbossche 