Using subrequests prevents some context being used

I'm using view_mode_page for a display mode that shows views within layout builder. The views use a group id as a contextual filter. With view_mode_page rendering the content as a subrequest, the group context gets lost because the route parameters are just entity type, entity id and view mode.

I've prepared a patch that changes view_mode_page from using a subrequest to setting up routes for the aliases. The routes essentially clone the entity's canonical route, except for the view mode.