Item hierarchy should be maintained when adding to menu

[JohnONolan]

Situation:

Create a hierarchy of categories or pages and go to create a custom menu. In the meta boxes on the left hand side, the categories and pages are shown in hierarchical arrangement. Select all categories (for example) and add to menu.

Expected behaviour:

All links are added to custom menu and the hierarchy is maintained appropriately

Actual behaviour:

Hierarchy is lost and all menu items are top-level

This was originally raised by Jane in #17029 however the changeset in the ticket only applies to showing hierarchy in the meta boxes and doesn't cover maintaining hierarchy when adding to menu.

Strongly agree with this.

Strongly agree with this.