[FLINK-38832][table-planner] Push down single column when using count star

[xuyangzhong]

What is the purpose of the change

Prunes the input columns of a LogicalAggregate representing COUNT(*) (i. e. no group keys, a single COUNT aggregate call with no arguments and no filter) by inserting a project of a constant literal 0 between the aggregate and its input.
This avoids reading all columns from the source when only counting rows.

Before:
LogicalAggregate(group=[{}], EXPR$0=[COUNT()])
+- SomeInput

After:
LogicalAggregate(group=[{}], EXPR$0=[COUNT()])
+- LogicalProject($f0=[0])
+- SomeInput

Brief change log

• Add a new rule PruneCountStarInputRule
• Remove part of unreachable codes in FlinkRelBuilder#aggregate
• Update plans about existent tests

Verifying this change

Existent tests can cover this change.

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, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented?

[flinkbot]

CI report:

• a0484dc Azure: SUCCESS

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