EntityUrlLookup currently only has 1 method, getFullUrl as that is all we have needed so far.
Moving forward we also need to be able to get a relative / local url for an entity ID.

We decided that the best way to approach this would be to continue to have a FULL method, but also have a more generic getUrl method that would return a local or full url based on the context.

These behaviours should be documented in the phpdoc of the interface.

This will be used in T251242 where the formatter needs both / either relative / full url (for either federated props or local props)