[ticket/13061] Replace the service event.subscriber_loader by a compiler pass

PHPBB3-13061
Merge pull request #2948 from Nicofuma/ticket/13061

[ticket/13061] Replace the service event.subscriber_loader by a compiler pass

* Nicofuma/ticket/13061:
  [ticket/13061] Replace the service event.subscriber_loader by a compiler pass
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/13061] Replace the service event.subscriber_loader by a compiler pass