Pass return type to the accumulator state factory in aggregates

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
I am working to expose "selector functions" in IOx, See https://github.com/influxdata/influxdb_iox/pull/5606 https://github.com/influxdata/influxdb_iox/issues/5528

I want to be able to call an aggregate that has different types based on its input arguments. There is sufficient flexibility in the return_type and state type factories, but the accumulator factory is not passed the output type, so I can't figure out any way to instantiate the correct internal implementation.

I can't defer the choice until runtime either because if no rows go in, I need to know how to produce the appropriate type of NULL value, which depends on the output type.

Describe the solution you'd like
Pass the return data type as an argument to the accumulator factory, consistent with the state type factory

Describe alternatives you've considered
I tried various ways around this and could not find any :(

Additional context
https://github.com/influxdata/influxdb_iox/pull/5606 https://github.com/influxdata/influxdb_iox/issues/5528