TYP: Add type hint for DataFrame.T and certain array types
While updating a large pandas codebase with type coverage to 1.0, I noticed that `DataFrame.transpose()` is annotated to return `DataFrame` while `DataFrame.T` has no such hint. This PR also adds hints in a few places other places where they're trivial.

The definition of `pandas.core.base.IndexOpsMixIn.transpose` (and associated `.T`) currently do not have any type hints and fixing this seems more complicated, meaning `Index.T` and `Series.T` are not fixed by this PR.

Happy to amend to cover that case if anyone has suggestions, but I believe `DataFrame.T` to be the vast majority of usage.

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

thanks @qwhelan 