ENH: Select numeric ExtensionDtypes with DataFrame.select_dtypes
- [x] closes #35340
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @andrewgsavage! 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 2020-10-19 13:14:33 UTC This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. @andrewgsavage can you merge master to resolve conflicts. Also needs a release note. (put in doc\source\whatsnew\v1.2.0.rst for now, but my need to moved as 1.2rc is scheduled before the end of the month) Closing in favor of #38246