TST: Add ExtensionArray base tests for ops between pandas objects and EAs
We should document the expected behavior for binary operations between ExtensionArrays and pandas' own objects (Series, DataFrame, Index). We should update our own EAs to match the docs.

```python
In [4]: integer_array([1, 2]) + pd.Series([1, 2])
Out[4]: IntegerArray([2, 4], dtype='Int64')
```

`Out[4]` should be a Series with "Int64" dtype, to match the behavior of ndarray + series.

We've documented this, but need to test between series, index, dataframe, and the array class

https://github.com/pandas-dev/pandas/blob/6bf6cd2fe991f4f57e045e1f28a9dff860b72b37/pandas/tests/extension/base/ops.py#L83-L88