bpo-45019: Do some cleanup related to frozen modules. (gh-28319)

There are a few things I missed in gh-27980. This is a follow-up that will make subsequent PRs cleaner. It includes fixes to tests and tools that reference the frozen modules.

https://bugs.python.org/issue45019

Tools/scripts/generate_stdlib_module_names.py

@@ -117,9 +117,19 @@ def list_frozen(names):
         cmd = ' '.join(args)
         print(f"{cmd} failed with exitcode {exitcode}")
         sys.exit(exitcode)
+    submodules = set()
     for line in proc.stdout.splitlines():
         name = line.strip()
-        names.add(name)
+        if '.' in name:
+            submodules.add(name)
+        else:
+            names.add(name)
+    # Make sure all frozen submodules have a known parent.
+    for name in list(submodules):
+        if name.partition('.')[0] in names:
+            submodules.remove(name)
+    if submodules:
+        raise Exception(f'unexpected frozen submodules: {sorted(submodules)}')
 
 
 def list_modules():