MongoDB 3.8 will reply with a document stream to query-like commands such as "find" and "aggregate". This will require a spec for all drivers about how to negotiate the wire protocol upgrade. Handle document streams from OP_MSG replies. Update mongoc_apm_command_succeeded_init and mongoc_apm_command_succeeded_get_documents to expose the document sequence directly from OP_MSG instead of simulating it from a reply body.