All interfaces are documented at https://docs.google.com/document/d/1aZxeZ2FIh9Sn1KYotp-ac4G2AjzrT4hDKkChe4hiFpM/edit?pli=1&tab=t.0#heading=h.5tiwgvviizy5. 

Included in scope:

1. ChangeStreamReaderBuilder interface
2. ChangeStreamShardTargeter interface
3. Class ChangeStream with structures needed to implement the interface (methods getChangeStreamType() etc.)
4. Type ChangeStreamType.
5. ChangeStreamReaderContext interface.
6. Type ShardTargeterDecision.
7. ChangeStreamReaderBuilder programmable mock implementations (to support testing of _internalChangeStreamHandleTopologyChangeV2 stage).