Python: Add test cases

I debated whether to add a
`MISSING: use=moduleImport("builtins").getMember("print").getReturn()`
annotation to the last line.

Ultimately, I decided to add it, as we likely _do_ want this information
to propagate into inner functions (even if the value of `var2` may
change before `func4` is called).

python/ql/test/experimental/dataflow/ApiGraphs/test_import_star.py

@@ -23,3 +23,13 @@ def foo():
 def quux():
     global non_module_member
     non_module_member = 5
+
+def func1():
+    var() #$ use=moduleImport("unknown").getMember("var").getReturn()
+    def func2():
+        var = "FOO"
+
+def func3():
+    var2 = print #$ use=moduleImport("builtins").getMember("print")
+    def func4():
+        var2() #$ MISSING: use=moduleImport("builtins").getMember("print").getReturn()