BUG: Fix #15344 by backporting ujson usage of PEP 393 API
Make use of the PEP 393 API to avoid expanding single byte ascii characters into four byte unicode characters when encoding objects to json.

 - [ ] closes #15344
 - [ ] tests added / passed
 - [ ] passes ``git diff upstream/master | flake8 --diff``
 - [ ] whatsnew entry
