The changes for GODRIVER-1752 require the ClientEncryption type to internally use the transformBsoncoreDocument helper. Because ClientEncryption isn't configured with a BSON registry, the changes in that ticket temporarily use bson.DefaultRegistry. Once that's merged, we should figure out the actual semantics and implement them in the same release as GODRIVER-1752.

This will probably require adding a ClientEncryption option to specify a Registry. If that option isn't set, we'll have to decide if we want to default to bson.DefaultRegistry or to the key vault Client's Registry.