PERF: fix long string representation
- [x] closes #36636
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

- Fix long string representation for large dataframes.
- Eliminate for loop, which was filtering out the proper rows/columns to be displayed.
- Revert to the original implementation with concat-ing head+tail and left+right parts.