Python: Add missing hidden flow

The easiest way to implement this was to change the definition of
`module_export` to account for chains of `import *`. We reuse the
machinery from `ImportStar.qll` for this, naturally.

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowPrivate.qll

@@ -2,6 +2,7 @@ private import python
 private import DataFlowPublic
 import semmle.python.SpecialMethods
 private import semmle.python.essa.SsaCompute
+private import semmle.python.dataflow.new.internal.ImportStar
 
 /** Gets the callable in which this node occurs. */
 DataFlowCallable nodeGetEnclosingCallable(Node n) { result = n.getEnclosingCallable() }
@@ -927,7 +928,7 @@ predicate jumpStep(Node nodeFrom, Node nodeTo) {
 private predicate module_export(Module m, string name, CfgNode defn) {
   exists(EssaVariable v |
     v.getName() = name and
-    v.getAUse() = m.getANormalExit()
+    v.getAUse() = ImportStar::getStarImported*(m).getANormalExit()
   |
     defn.getNode() = v.getDefinition().(AssignmentDefinition).getValue()
     or