make the module closer referenceable

This is all that is required to make module reference ordering work
during apply, by adding and edge to the nodeCloseModule node, which will
be the last node evaluated in the module.

terraform/node_module_expand.go

@@ -99,6 +99,23 @@ type nodeCloseModule struct {
 	Addr addrs.Module
 }
 
+var (
+	_ graphNodeModuleCloser  = (*nodeCloseModule)(nil)
+	_ GraphNodeReferenceable = (*nodeCloseModule)(nil)
+)
+
+func (n *nodeCloseModule) ModulePath() addrs.Module {
+	mod, _ := n.Addr.Call()
+	return mod
+}
+
+func (n *nodeCloseModule) ReferenceableAddrs() []addrs.Referenceable {
+	_, call := n.Addr.Call()
+	return []addrs.Referenceable{
+		call,
+	}
+}
+
 func (n *nodeCloseModule) Name() string {
 	if len(n.Addr) == 0 {
 		return "root"