message: Put VarHandleOp nodes in a separate group in the annotated graph dump; NFC
  This helps readability because typically a lot of the incoming edges into a
  cluster are resource variable ops.
diff: @@ -1176,6 +1176,8 @@ Status MarkForCompilationPass::RunImpl(
  if (absl::optional<absl::string_view> cluster_name =
  GetXlaClusterForNode(*n)) {
  n->set_name(absl::StrCat(*cluster_name, "/", n->name()));
  + } else if (n->type_string() == "VarHandleOp") {
  + n->set_name(absl::StrCat("varhandle/", n->name()));
  } else {
  // There is room for improvement here. In particular, it may help to
  // split these unclustered nodes into classes where every node in a
  