API: Allow other na values in StringArray Constructor
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [ ] whatsnew entry

around 20-30% perf regression compared to master on added benchmarks. Still faster than 1.3.x so the regression is not user visible if we merge this for 1.4.0.
really just a quick and dirty solution to unblock @jbrockmendel.
The best solution would be to go through ensure_string_array(which is what _from_sequence does), but that would take a lot of effort to avoid perf regressions(it seems like ensure_string_array does not type its ``arr`` arg and also takes in EA inputs? we should probably restrict to numpy arrays as suggested by a code comment in the stub file).

I'll open an issue as a follow-up.
> it seems like ensure_string_array does not type its arr arg and also takes in EA inputs

yah thats a pattern we should avoid.  IIRC there is a TODO in the code about that. gentle ping @jreback @jbrockmendel. @github-actions pre-commit. Hello @lithomas1! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:









There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2022-01-15 15:58:47 UTC @github-actions pre-commit. thanks @lithomas1 