Update references/relations after completing scope using notifications

[ronaldbarendse]

As mentioned in #20079 (review), the CMS currently updates all references in the document, media and member repositories by calling ContentRepositoryBase.PersistRelations() when inserting and updating them:

• DocumentRepository.PersistNewItem():

  Umbraco-CMS/src/Umbraco.Infrastructure/Persistence/Repositories/Implement/DocumentRepository.cs

  Line 1077 in 472be3d

  PersistRelations(entity);

• DocumentRepository.PersistUpdatedItem():

  Umbraco-CMS/src/Umbraco.Infrastructure/Persistence/Repositories/Implement/DocumentRepository.cs

  Line 1328 in 472be3d

  PersistRelations(entity);

• MediaRepository.PersistNewItem():

  Umbraco-CMS/src/Umbraco.Infrastructure/Persistence/Repositories/Implement/MediaRepository.cs

  Line 419 in 472be3d

  PersistRelations(entity);

• MediaRepository.PersistUpdatedItem():

  Umbraco-CMS/src/Umbraco.Infrastructure/Persistence/Repositories/Implement/MediaRepository.cs

  Line 481 in 472be3d

  PersistRelations(entity);

• MemberRepository.PersistNewItem():

  Umbraco-CMS/src/Umbraco.Infrastructure/Persistence/Repositories/Implement/MemberRepository.cs

  Line 791 in 472be3d

  PersistRelations(entity);

• MemberRepository.PersistUpdatedItem():

  Umbraco-CMS/src/Umbraco.Infrastructure/Persistence/Repositories/Implement/MemberRepository.cs

  Line 941 in 472be3d

  PersistRelations(entity);

This results in parsing all property data on every save using DataValueReferenceFactoryCollection.GetAllReferences() (for both edited and published values), even if no property data is changed. This results in an unnecessary performance penalty, especially if multiple saves/publishes are done within a single Umbraco scope (like Deploy does).

A bigger issue is timing: if the property data contains a reference to e.g. media, but that media isn't available yet, the CMS will not create the reference/relation. This is quite common when transferring content using Deploy: although related media items that don't exist yet will automatically be included in the transfer, there's no strict requirement for the media to be deployed first (compared to parent items that do need to exist first). Although Deploy could be updated to ensure the related media item is saved first, this can cause a cyclic dependency (when creating the TopoGraph).

One possible solution would be to update the references/relations after completing the scope using notifications. The notification handler would need to inherit from IDistributedNotificationHandler to ensure it's handled after e.g. Deploy operations.