ExtractNewRecordState should support inline ValueToKey functionality

The current ExtractNewRecordState isn't easy to use in conjunction with [ValueToKey|https://docs.confluent.io/platform/current/connect/transforms/valuetokey.html.]  The problem is that unless you configure ExtractNewRecordState to drop tombstones and to rewrite delete records, the ValueToKey transformation will throw an exception because it can't function on a record with a null value.

However, if you do so configure ExtractNewRecordState, then you need a third transformation after ValueToKey which will convert the records with "__delete:true" back to tombstones.

It would be much more convenient if ExtractNewRecordState could support changing the record key inline, since it has all the required information at hand.