32818 add attachments

- Added attachment handling to CDTMutableDocumentRevision via the attachments property
- Depercated old attachment API in CDTDatastore+attachments.h
- Created new Attachment CRUD tests based off AttachmentCRUD.m
Comment explaining logic: if attachment is unsaved, it must be new, so stream to blob store and add it to this revision. Otherwise it's an existing attachment and its details need to be copied forward for this revision.