fix(#3638315): report the depth limit only for component references

Past the paragraph depth limit, the publishing check reported unchecked text for any reference on the deepest component, including a reference to a node, and with fail_closed on it refused the save. It now reports the limit only when a reference past it points at a component, with the same component test the check and the content scan already use. A kernel test covers a node reference at the limit, and another checks that a save and a scan stop at the same depth