Implement optimizer hook for combining partial/final aggregate in AggregateExec #25928

Is your feature request related to a problem or challenge?

This is a follow-up cleanup for #25696

See this issue for the underlying idea (on another problem)

• Make AggregateExec state modeling and public updates safe #25563

We could do the similar refactor on CombinePartialFinalAggregate optimizer rule, here is the specific location for the refactor:

• https://github.com/apache/datafusion/pull/25696/changes#r4100893886

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