ENH: Add MultiIndex.dtypes
- [x] closes #37062 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Adds the .dtypes property to MultiIndex using the suggested implementation
@jreback Made the requested changes. Could you take a look? can you merge master > can you merge master

Done. Hello @skvrahul! 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 2020-12-08 18:24:25 UTC I've resolved conflicts. Should be good to merge with the base branch now. Made the requested changes and passing all tests. Should be okay to merge now
@jreback @arw2019  thanks @skvrahul very nice!