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.
Well, one of the motivations for the pull request was the ability to generate the URL alias by `contentId`.

The use case is the one I mentioned in the description: field value of a Relation field type only has a content ID. This is the only way to generate the URL alias for that content ID (apart from calling `ez_render_field`, ofcourse)