ENH: rolling rank followups
Followups from #43338

- [ ] tests for `groupy.rolling.rank`
- [ ] `dense` ranking method impl
- [ ] add `expanding` rank to asvs
- [ ] unify separate tiebreakers dicts in aggregations.pyx and algos.pyx: https://github.com/pandas-dev/pandas/pull/43338#discussion_r708248202