TYP: Annotated pandas/core/indexing.py
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

> lgtm. I think additional types as proposed by @jbrockmendel would be nice if not too much extra effort

The problem is that I don't know how to annotate them:( OK thanks @MomIsBestFriend . Sure can always add more types as you get more familiar with code base