Check various `__init__.pyi` files to align exports done in `pandas` source `__init__.py` files.

[Dr-Irv]

I just stumbled on a similar problem with pandas.io module. __init__.pyi is completely empty here, so none of the underlying modules are visible to type checkers.
This goes on deeper as well, because pandas.io.formats.__init__.pyi is also empty
I was interested in pandas.io.formats.style.Styler.
Would you like me to file a separate issue(s)?

Originally posted by @Molkree in #1221