Is there a use-case for serializing `BsonDocument`, `BsonArray` and `BsonValue` to non-BSON formats? For example, JSON? In practice, this is complex to implement, because KotlinX.Serialization doesn't support general serialization types which don't know the shape of the serialized element in advance. `BsonDocument` & co could contain arbitrary data. See [KotlinX.Serialization#1573](https://github.com/Kotlin/kotlinx.serialization/issues/1573).