Fixes sphinx-doc#10809

* the option autosummary_ignore_module_all when set to False adds members to module's members entry that will be used for autodoc, but otherwise it ignores it. As such, if a class is available in the __all__, it won't be generated.
* This commit aims at extending the __all__ handling not only to members, but also to corresponding attribute types (function, classes, exceptions, modules)
* In short, the imported_members option is set to True if the object has __all__ member and autosummary is set to have autosummary_ignore_module_all set to False

…odule_all is True

* When ignore_module_all is False, search for imported modules (possibly renamed) and in discovered modules, public modules are then the one mentioned in __all__
* In a more general usecase, skip all modules that are overwritten in the package namespace