BUG: Fix segfault on dir of a DataFrame with a unicode surrogate character in the column name
Return a `repr()` version if the column name string is not printable. This also means the the column name is not present in the output of `dir()`

- [x] closes #25509 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
