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.
The only real question I have here is how to handle the fact that main location may not exist:

From the issue:

> a Content OR a ContentInfo, in which case it generates the alias to the main Location, **if** there is one