pd.NA in object dtype
extract from https://github.com/pandas-dev/pandas/issues/32075#issuecomment-596735782

If we want to handle pd.NA in object dtype better, we will need to start using masks as well, and not rely on numpy behaviour. 

For example, also this is wrong:

```
In [9]: pd.Series([1, pd.NA], dtype=object) >= 1
Out[9]: 
0     True
1    False
dtype: bool
```


Related issues:

* https://github.com/pandas-dev/pandas/issues/32075 (replace not working)
* https://github.com/pandas-dev/pandas/issues/33065 (wrong truncated repr)
* https://github.com/pandas-dev/pandas/issues/33066 (wrong comparison operations)
* https://github.com/pandas-dev/pandas/issues/34497 (indexing with duplicates)