BUG: IntervalIndex.putmask with datetimelike dtypes
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Implements `NDArrayBackedExtensionArray.putmask` which will hopefully be rolled into `__array_function__` to simplify a bunch of code.