ENH: dtype('bool') ndarray or Series coerced to dtype('int') in qcut GH20303

- [x] closes #20303 
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Currently, passing a `dtype('bool')` `ndarray` or `Series` as argument to `qcut` raises a `TypeError`.  As was suggested in #20303, now `_coerce_to_type` also coerces `bool` types to `int`. 