ENH: indexing and __getitem__ of dataframe and series accept zerodim integer np.array as int
- [ ] closes #24919
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

- Now the `df.iloc`, `df.loc`, `df.__getitem__` accepts zero dim integer numpy  array, as follows:

```python
df.iloc[np.array(0)]
df.loc[np.array(0)]
df[np.array(0)]
```
- I think this change possibly harms the performance of df.iloc