Keep imports alphabetically sorted and their order homogeneous across
Python source files.
The isort project has more feature and is more active than the
flake8-import-order plugin.
Most issues caught were simply import ordering from the same module.
Where imports were purposefully placed out of order, tag with
isort:skip.
In #7651, autodoc stops to undecorate the functions on getting the
signature from the callables. But some kinds of decorators conceals
the correct signature because they pass through their arguments via
`(*args, **kwargs)`.
This restarts to undecorate the functions again as before #7651.
