terraform: add edge for missing providers

terraform/test-fixtures/plan-module-destroy-multivar/main.tf

@@ -2,4 +2,3 @@ module "child" {
   source = "./child"
   instance_count = "2"
 }
-

terraform/transform_provider.go

@@ -218,6 +218,11 @@ func (n *graphNodeMissingProvider) EvalTree() EvalNode {
 	return ProviderEvalTree(n.ProviderNameValue, nil)
 }
 
+// GraphNodeDependable impl.
+func (n *graphNodeMissingProvider) DependableName() []string {
+	return []string{n.Name()}
+}
+
 func (n *graphNodeMissingProvider) ProviderName() string {
 	return n.ProviderNameValue
 }
@@ -280,6 +285,11 @@ func (n *graphNodeMissingProviderFlat) ProviderName() string {
 		n.graphNodeMissingProvider.ProviderName())
 }
 
+// GraphNodeDependable impl.
+func (n *graphNodeMissingProviderFlat) DependableName() []string {
+	return []string{n.Name()}
+}
+
 func (n *graphNodeMissingProviderFlat) DependentOn() []string {
 	var result []string