REAL column values are omitted if value is an exact integer

This only happens with wal2json. If we receive a JSON integer, rawValue.asFloat() returns null in Wal2JsonReplicationMessage.getValue(). This might be the same for other non-integer numeric types, too. We should add a test for all non-integer columns with an exact integer value to make sure this is addressed everywhere.

Originally brought up on the mailing list.