C API: Add PyImport_AddModuleRef() function

[vstinner]

The C API PyImport_AddModule() returns a borrowed reference using a special dance added by commit 4db8988 of issue #86160:

 PyObject *ref = PyWeakref_NewRef(mod, NULL);
 Py_DECREF(mod);
 if (ref == NULL) {
 return NULL;
 }
 mod = PyWeakref_GetObject(ref);
 Py_DECREF(ref);

Borrowed references are bad:

• "Functions must not return borrowed references" says https://devguide.python.org/developer-workflow/c-api/index.html
• Unclear lifetimes of borrowed references capi-workgroup/problems#5

I proposed to:

• Add a new PyImport_AddModuleRef(const char *name) function, similar to PyImport_AddModule() but return a strong reference
• Deprecate PyImport_AddModule() and PyImport_AddModuleObject()

Linked PRs

• gh-105922: Add PyImport_AddModuleRef() function #105923
• gh-105922: Refactor PyRun_InteractiveOneObjectEx() #105925
• gh-105922: PyImport_AddModule() uses Py_DECREF() #105998
• gh-105922: Use PyImport_AddModuleRef() function #105999