REF: dispatch DTI/TDI setops to RangeIndex
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [ ] whatsnew entry

Includes #44019 (but not that whatsnew)

I'm optimistic we can eventually dispatch all the relevant cases and then can get rid of the special-cased _fast_union/_fast_intersect.