REF: move values_for_json to EA
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Added docstring.  Not confident enough in how this works to add tests yet @WillAyd OK here? I don't know that I see the vision for how this will actually work with JSON arguments (i.e. date formatting) but no objection to it either Unless there are more comments, I'm planning to merge later this week. Thanks @jbrockmendel 