BUG: Index.get_slice_bounds does not accept datetime.date or tz naive datetime.datetimes
- [x] closes #35690
- [x] closes #34077
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

This method appeared under tested so added some additional tests for numeric and object `Index`

Just commented on #35690, the upshot of which is that I think the current behavior is correct. Hello @mroeschke! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:









There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-09-02 05:43:44 UTC lgtm @mroeschke 

ideally we *also* test via ```.loc[]``` for these behaviors (we likey have some already tested); but as a followup is fine. See comment [above](https://github.com/pandas-dev/pandas/pull/35848#issuecomment-679397568), this PR should not be merged.