[FLINK-5915] [table] forward the entire aggregate ArgList to aggregate runtime functions

[shaoxuan-wang]

This PR partially solved "FLINK-5915 Add support for the aggregate on multi fields".
The roadmap of UDAGG would be 1. codeGen all the runtime aggregate functions; 2. add UDAGG tableAPI interface.
I would like to kick this PR off earlier as: a) we can finalize the runtime function while doing the codeGen; b) as more and more (over) aggregates are implemented, it would be good if we can finalize the interface and share library to the stage (as we planned) as earlier as possible.

Note that: though the entire aggregate ArgList is forwarded to the runtime function, for the functions that have not been codeGened, we will still support only one column aggregate input.

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[fhueske]

Can we use an Array[Int] instead of a List[Integer]?

Scala Int is compiled to Java int primitive. java.lang.Integer is a boxed type.
Also an array access is faster than a List.get() access (ArrayList.get() would be a bit better).

[fhueske]

The change looks good in general. I'd prefer to use an array instead of a List though.
What do you think @shaoxuan-wang?

[shaoxuan-wang]

Thanks @fhueske, I overlooked a list is not always an arraylist. I change it to scala array, but keep the type as integer, as this is type returned (and not easy to be casted to Int) from aggregateCall.getArgList. I updated PR and also rebased to the master (as I noticed there are a few over aggregates have been recently merged), so it will be easier for you to merge.

[fhueske]

Thanks @shaoxuan-wang, I found a way to cast the Integer to Int. Will change that and merge the PR.

Thanks, Fabian