Re-calculate the starting change log offset after the new table added

In mysql cdc, re-calculate the starting binlog offset after the new table added in MySqlBinlogSplit#appendFinishedSplitInfos, while there lack of same action in StreamSplit#appendFinishedSplitInfos. This will cause data loss if any newly added table snapshot split's highwatermark is smaller.

Some unstable test problem occurs because of it.