path alias entities should be listed in relationships

Problem/Motivation

Path alias entities are references from nodes (or other entities), and should be listed in the references.

This would be helped by #3008058: Convert the computed path item field type to a regular entity reference field but it doesn't need to wait for it.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet