REF: separate flex from non-flex DataFrame ops
- [x] closes #36796
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Unless supporting this is intentional, in which case we should deprecate and explicitly implement flex-bool operations.

If/when this is done, we can stop passing `special` and even `cls`.