CLN import from pandas.core.arrays when possible
- [ ] closes #xxxx
- [X] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

`pandas.core.arrays.__init__.py` imports some classes by default, so other classes can import directly from `pandas.core.arrays` instead of accessing the specific files