BUG: Fixed inconsistent offset behavior for series #43784
- [ ] closes #43784 
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [x] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

I'm not exactly sure how these extra commits got into this new PR, but I fixed the file conflicts so that those extra changes are gone. I realize `test_shift_across_dst` in `test_offsets_properties.py` fails right now and I am working on a fix for that. There seems to be a test failing called `test_reindexing_with_float64_NA_log` in `test_reindex.py`, but I've run this test without my code change, and it ends up failing anyways, so I don't think this change is to blame. @mroeschke I've changed the check to take into account user-created subclasses by removing the type check in the if statement.  I've also changed the `_use_relativedelta` field in the existing subclasses to match their behavior. This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. Thanks for the pull request, but it appears to have gone stale. If interested in continuing, please merge in the main branch, address any review comments and/or failing tests, and we can reopen.