Currently, the request object is embedded directly in the coordinator document, which creates the need to acquire `_docMutex` each time it is accessed from the coordinator. There is a mismatch between the name of the only field in the original request document (to) mongo/src/mongo/s/request_types/move_primary.idl and the coordinator document (toShardId) mongo/src/mongo/db/s/move_primary_coordinator_document.idl. Changing the name of the coordinator document field to match the request would allow to simply chain the request document inside the coordinator document, and thus it could be copied on construction to avoid contention later. This change should take into account version update issues.