inspect.docs: Fix indentation and version-added for Signature.from_callable
inspect.docs: Document that Signature and Parameter are now picklable (issue #20726)
inspect: Update docstrings; Rename _signature_internal to _signature_from_callable.
Minor readability improvement.
merge
Issue #21097: Move test_namespace_pkgs into test_importlib.
Issue #21097: Move test_namespace_pkgs into test_importlib.
Null merge from 3.4.
Fix doc typo.