bpo-35181: Correct importlib documentation for some module attributes (GH-15190)

bpo-35181: Correct importlib documentation for some module attributes (GH-15190)

@ericsnowcurrently This PR will change the following:

In the library documentation importlib.rst:

- `module.__package__` can be `module.__name__` for packages;
- `spec.parent` can be `spec.__name__` for packages;
- `spec.loader` is not `None` for namespaces packages.

In the language documentation import.rst:

- `spec.loader` is not `None` for namespace packages.

Automerge-Triggered-By: GH:warsaw
(cherry picked from commit 27f1bd8787d24ac53cc3dc6ea5eb00b8a3499839)

Co-authored-by: Géry Ogam <gery.ogam@gmail.com>