REF: Move rest of aggregation into apply
- [x] 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

Purely a move. I have a PR just about ready to start tackling #41112, but it needs to touch some of the renamer code. It'd be nice to have it all in `core.apply`, and logically makes sense to go there.

thanks @rhshadrach 