Don't add arbitrary non-field menu to $node

Problem/Motivation

+++ b/core/modules/menu_ui/menu_ui.module
@@ -548,18 +408,24 @@ function menu_ui_form_node_form_alter(&$form, $form_state) {
+      // Have to tack this onto the node so we can save it later when we have a
+      // a node ID for any new node.
+      $node->menu = $definition;

Although $node->menu is a preexisting condition of HEAD, can we open an issue and add an @todo here to remove that? In D8, we shouldn't be adding arbitrary non-field properties to content entities.

Proposed resolution

Create a menu link field and kill this whole set of code?

Or figure out some way core supports arbitrary data properly?

Remaining tasks

User interface changes

API changes