In json_event_deserializer.cppp, we should always use the bsoncxx from json. It supports the entire JSON spec.

See this comment in fromjson: https://github.com/mongodb/mongo/blob/ccaadff2491cd1758157358101df1636a3da9c96/src/mongo/bson/json.cpp#L1396

Also, according to Mark, most uses of fromjson are only in test cases: https://mongodb.slack.com/archives/C0V2Z88D8/p1695414350852849?thread_ts=1695413685.467989&cid=C0V2Z88D8