BUG: #35830 Restore index & slice by date to DatetimeIndex
#35830 DatetimeIndex has supported indexing by date for many many years. This was broken after 1.0.5. This attempts to restore support by converting a date to Timestamp in `get_loc` and `_validate_searchsorted_value`. This restores indexing slicing, and  `asof` but  `in` does not work. It seems the best solution would be to do the conversion in `DatetimeLikeArrayMixin._validate_scalar` but this breaks a test looking for an expected `FutureWarning` in `TestDataFrameIndexing::test_loc_setitem_datetime_coercion` warning a `Timestamp` can't be compared to a `date`

- [x] closes #35830
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

I can add more tests for slicing and asof (they work) if this will be considered for merging This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. Closing as it appears this PR has gotten stale. Let us know if you'd like to continue adding a deprecation warning for this behavior and we'd be happy to reopen.