PDEP6 implementation pt 3: block.where
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

this one causes errors for
```python
data1 = [[1, 2], [3, 4]]
data2 = [[0.5, 6], [7, 8]]
df1 = DataFrame(np.array(data1))
df2 = DataFrame(np.array(data2))
df = concat([df1, df2], axis=1)
df[df>2]
```
, I'll dig deeper but it might be better to leave it out (at least for now)