check walkDestroy to help DestroyEdgeTransformer

In a heavily-connected graph with lots of inter-dependent providers, the
cycle checks for destroy edges across providers can seriously impact
performance. Since the specific cases we need to avoid will involve
create/update nodes, skip the extra checks during a full destroy
operation. Once we find a way to better track these dependencies, the
transformer will not need to do the cycle checks in the first place.

internal/terraform/graph_builder_apply.go

@@ -144,7 +144,8 @@ func (b *ApplyGraphBuilder) Steps() []GraphTransformer {
 
 		// Destruction ordering
 		&DestroyEdgeTransformer{
-			Changes: b.Changes,
+			Changes:   b.Changes,
+			Operation: b.Operation,
 		},
 		&CBDEdgeTransformer{
 			Config: b.Config,

internal/terraform/transform_destroy_edge.go

@@ -46,6 +46,11 @@ type DestroyEdgeTransformer struct {
 	// DiffTransformer which was intended to be the only transformer operating
 	// from the change set.
 	Changes *plans.Changes
+
+	// FIXME: Operation will not be needed here one we can better track
+	// inter-provider dependencies and remove the cycle checks in
+	// tryInterProviderDestroyEdge.
+	Operation walkOperation
 }
 
 // tryInterProviderDestroyEdge checks if we're inserting a destroy edge
@@ -81,6 +86,12 @@ func (t *DestroyEdgeTransformer) tryInterProviderDestroyEdge(g *Graph, from, to
 	e := dag.BasicEdge(from, to)
 	g.Connect(e)
 
+	// If this is a complete destroy operation, then there are no create/update
+	// nodes to worry about and we can accept the edge without deeper inspection.
+	if t.Operation == walkDestroy {
+		return
+	}
+
 	// getComparableProvider inspects the node to try and get the most precise
 	// description of the provider being used to help determine if 2 nodes are
 	// from the same provider instance.