Support and require Drupal 8.5.0

Bojanz made an overview of some interesting issues already in the equivalent issue for Drupal Commerce #2950745: Require Drupal 8.5.x

Drupal 8.5.0 has released today and all sites are encouraged to update. We should evaluate what changes have been made since 8.4.0 and see which we can utilise. That'll also require setting Drupal Core 8.5.0 as a requirement for the module.