Reset display folded for an instanced scene if editable children is toggled off

This avoids the display folded flag needlessly getting into the scene file (potentially forever) and also gives more visual feedback if the user re-enables editable children so it will display unfolded at first.

scene/main/node.cpp

@@ -1357,10 +1357,14 @@ void Node::set_editable_instance(Node *p_node, bool p_editable) {
 	ERR_FAIL_NULL(p_node);
 	ERR_FAIL_COND(!is_a_parent_of(p_node));
 	NodePath p = get_path_to(p_node);
-	if (!p_editable)
+	if (!p_editable) {
 		data.editable_instances.erase(p);
-	else
+		// Avoid this flag being needlessly saved;
+		// also give more visual feedback if editable children is reenabled
+		set_display_folded(false);
+	} else {
 		data.editable_instances[p] = true;
+	}
 }
 
 bool Node::is_editable_instance(Node *p_node) const {