title: @StateObject for a NSManagedObject without context not publishing changes
body: <p>Like in a lot of apps, I have a list of items (populated by a Core Data fetch request), a sheet to create new items, and a sheet to edit an item when tapping on a row in my list. I'm trying to unify both forms to create and edit an update, and put the cancel / save logic in a superview of the form.</p>
  <p>So I've something like this:</p>
  <ul>
  <li>ListView: a list with row populated by a Core Data fetch request</li>
  <li>AddView: a NavigationView with the FormView embed + cancel and save button</li>
  <li>EditView: a NavigationView with the FormView embed + cancel and save button</li>
  <li>FormView: a TextField to update the name of the item</li>
  </ul>
  <p>In the init() for the AddView, I create a new NSManagedObject without any context (I do that because I don't want my ListView to be updated when I create a new item in the AddView, but only when I save this item -&gt; alternative could be to use a child context, or filter the fetch request results based on the isInserted or objectID.isTemporaryID of the return objects). AddView contains a NavigationView with the FormView embed, a cancel button, and a save button. This save button is disabled based on a computed property on the managed object (name for the object can't be nil).</p>
  <p>In the EditView, I pass the item that was tapped from the ListView. This item is an existing NSManagedObject attached to the main viewContext of the app (coming from the fetch request of the ListView). EditView contains a NavigationView with the FormView embed, a cancel button and a save button (exactly like the AddView). This save button is also disabled based on the same computed property.</p>
  <p>My issue is that when I update the name of the item from the TextField in my FormView, the condition to enable / disable the save button is not working for the AddView (this AddView is actually not refreshed when I change the item name from the FormView) but working for the EditView (this EditView is refreshed when I change the item name from the FormView). If I attach a context to the new NSManagedObject in the init() of the AddView, the condition is working like in the EditView.</p>
  <p>So it appears that a NSManagedObject without any context is not observed by SwiftUI? Am I missing anything or is that a bug?</p>