PERF: to speed up rendering of styler
see https://github.com/pandas-dev/pandas/issues/19917#issuecomment-646209895

- [x] closes #19917
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
