Fix EZP-22735: Make {{ path( 'ez_urlalias' ) }} polymorphic

A fix for already existing issue at JIRA: https://jira.ez.no/browse/EZP-22735

Common usecase is to generate an URL to content in Relation field value.
> Maybe we should consider (instead?) exposing ContentInfo on relation field types, like is the case on Relation object. 

Yeah, that would be something else.

RelationList would benefit from it also greatly (not considering the issue that together with object ID, legacy stored node ID selected in `/content/browse`, instead of main one as the new stack does)