BUG: crosstab with duplicate column or index labels
- [x] closes #22529
- [x] tests added / passed
- [x] passes black pandas
- [x] passes git diff upstream/master -u -- "*.py" | flake8 --diff
- [x] whatsnew entry

Picking up from #28474 

cc @jreback in case this can go in in time for 1.2