BUG: Perform i8 conversion for datetimelike IntervalTree queries
- [X] closes #20636
- [X] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] whatsnew entry

I've seen a few complaints about this on StackOverflow, so wanted to get this into 0.24.0 before I try implementing larger changes like the new behavior specs and interval accessor.