Various docstring fixes
- [x] xref #27976
- [x] tests added / passed - Didn't run all tests, only those concerning the issue (`./scripts/validate_docstrings.py pandas.Series.drop --errors=PR02`)

- [x] passes `black pandas` - Only docstrings were edited, so there were no major changes 
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] ~~whatsnew entry~~ -  Not needed, only docs changed
General fixes to the documentation in different places. I discovered that the root of many of the conflicts lies in decorators. We might need to re-evaluate how we're getting the signature of functions in the validation script. 

First time submitting a PR! Let me know if I need to do anything, or if there's anything I should do differently next time :)