[SPARK-18147][SQL] do not fail for very complex aggregator result type

## What changes were proposed in this pull request?

~In `TypedAggregateExpression.evaluateExpression`, we may create `ReferenceToExpressions` with `CreateStruct`, and `CreateStruct` may generate too many codes and split them into several methods.  `ReferenceToExpressions` will replace `BoundReference` in `CreateStruct` with `LambdaVariable`, which can only be used as local variables and doesn't work if we split the generated code.~

It's already fixed by #15693 , this pr adds regression test

## How was this patch tested?

new test in `DatasetAggregatorSuite`

Author: Wenchen Fan <wenchen@databricks.com>

Closes #15807 from cloud-fan/typed-agg.