After PM-1950, there are an increasing number of places where we write a no-op oplog message to signify to change streams that a particular event has occurred. Most of these places are now named notifyChangeStreamsOn* but are scattered throughout the code. We should make sure that ALL such no-op writers are named notifyChangeStreamsOn (e.g. the shardCollection no-op writer is currently just called _writeOplogMessage, the reshardBegin and reshardDoneCatchUp events are not in separate functions at all) and consolidate these into a dedicated library and API.