Fix EZP-23222: LanguageSwitcher does not work in content preview

JIRA: https://jira.ez.no/browse/EZP-23222

When `ez_route()` is used in content preview, the request will fail:
`RouteNotFoundException: None of the chained routers were able to generate route: Route '' not found `

This happens because PreviewController does not specify the route, only the controller.
Fix by passing the location route (`_ezpublishLocation`) and required `locationId` to the new internal request.