BUG: upcasting on reshaping ops #13247
Only rebasing and fixing the merge conflicts
Original work done by: @jennolsen84
Original branch: https://github.com/jennolsen84/pandas/tree/concatnan
Original PR: #13337 

 - [x] closes #13247
 - [x] tests added / passed
 - [x] passes ``git diff upstream/master | flake8 --diff``
 - [x] whatsnew entry
