[Editor] Fix undoing an editor deletion (bug 1886959)

The original bug was because the parent was null when trying to show
an highlight annotation which led to an exception.
That led me to think about having some null/non-null parent when removing
an editor: it's a mess especially if a destroyed parent is still attached
to an editor. Consequently, this patch always sets the parent to null when
deleting the editor.

src/display/editor/tools.js

@@ -1713,6 +1713,7 @@ class AnnotationEditorUIManager {
       layer.addOrRebuild(editor);
     } else {
       this.addEditor(editor);
+      this.addToAnnotationStorage(editor);
     }
   }