[FLINK-7776][TableAPI & SQL] do not emit duplicated records in group aggregation

[Xpray]

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What is the purpose of the change

to improve performance by stop collecting duplicated records

Brief change log

if current row is same with previous row, then collect nothing

Verifying this change

This change is already covered by existing tests, such as (please describe tests).

AggregateITCase.testRemoveDuplicateRecordsWithUpsertSink

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: no

Documentation

• Does this pull request introduce a new feature? no

[fhueske]

Thanks for the PR @Xpray.
It's good to merge.
I'll adapt the comment before merging.

Thanks, Fabian

[fhueske]

I'd remove the "and we may have to emit retractions" part of the comment as this is not reflected by the condition.

[Xpray]

I've removed this comment.

[fhueske]

Merging