Python: Add "enclosing callable" for ModuleVariableNode

I've named this `DataFlowModuleScope` since it's not really a
callable (and all of the relevant methods are empty anyway).

python/ql/src/experimental/dataflow/internal/DataFlowPrivate.qll

@@ -185,7 +185,8 @@ private Node update(Node node) {
  */
 newtype TDataFlowCallable =
   TCallableValue(CallableValue callable) or
-  TClassValue(ClassValue c)
+  TClassValue(ClassValue c) or
+  TModule(Module m)
 
 /** Represents a callable */
 abstract class DataFlowCallable extends TDataFlowCallable {
@@ -239,6 +240,22 @@ class DataFlowClassValue extends DataFlowCallable, TClassValue {
   override string getName() { result = c.getName() }
 }
 
+class DataFlowModuleScope extends DataFlowCallable, TModule {
+  Module mod;
+
+  DataFlowModuleScope() { this = TModule(mod) }
+
+  override string toString() { result = mod.toString() }
+
+  override CallNode getACall() { none() }
+
+  override Scope getScope() { result = mod }
+
+  override NameNode getParameter(int n) { none() }
+
+  override string getName() { result = mod.getName() }
+}
+
 newtype TDataFlowCall =
   TCallNode(CallNode call) or
   TSpecialCall(SpecialMethodCallNode special)

python/ql/src/experimental/dataflow/internal/DataFlowPublic.qll

@@ -177,6 +177,10 @@ class ModuleVariableNode extends Node, TModuleVariableNode {
       result.asVar().getDefinition().(EssaNodeDefinition).definedBy(var, defn)
     )
   }
+
+  override DataFlowCallable getEnclosingCallable() { result.(DataFlowModuleScope).getScope() = mod }
+
+  override Location getLocation() { result = mod.getLocation() }
 }
 
 /**