DEPR: Rolling.win_type returning freq & is_datetimelike
- [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
- [x] whatsnew entry

xref: https://github.com/pandas-dev/pandas/pull/38641#issuecomment-754118989
xref: https://github.com/pandas-dev/pandas/pull/38664/files#r551419130