bpo-45020: Add more test cases for frozen modules. (gh-28664)

I've added a number of test-only modules. Some of those cases are covered by the recently frozen stdlib modules (and some will be once we add encodings back in). However, I figured we'd play it safe by having a set of modules guaranteed to be there during tests.

https://bugs.python.org/issue45020

Lib/__phello__/spam.py

@@ -0,0 +1,7 @@
+initialized = True
+
+def main():
+    print("Hello world!")
+
+if __name__ == '__main__':
+    main()