BUG: retain extension dtypes in transpose
I'll have to look through the issues to see what this closes.

- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

> but can you check the output of

It looks like df.dtypes[0] == df.dtypes[1] == df.T.dtypes[0] == df.T.dtypes[1].  Is this the desired behavior? I believe so. Could you add a test case for unordered categories with differing orders? https://github.com/pandas-dev/pandas/pull/28048#pullrequestreview-280471818 will do also see if you can find any issues this solves (e.g. likely Datetime w/timezone transpose we have a couple of issues IIRC) & needs a whatsnew note. Closing to clear the queue.  The Right Way to do this will be to allow 2D EA. reopened and rebase closing in favor of #30091.