Improved API for registering platform entity services

Platform entity services should be registered by calling the helper service.async_register_platform_entity_service from the integration's async_setup instead of calling platform.async_register_entity_service during platform set up.

Existing integrations should be migrated to the new API to ensure loading the services does not depend on platform setup.

For examples of migrating, see core PR 152172 and core PR 152047.