Change Accumulator::evaluate and Accumulator::state to take &mut self #8934

Is your feature request related to a problem or challenge?

As part of #8849, I wanted to build up the output state (the distinct string values) during accumulation and then generate output directly (without a copy)

However, I couldn't implement a zero copy algorithm because evaluate and merge take a &self not a &mut self (well I worked around it with a Mutex 🤮 ).

The need to copy intermediate state likely doesn't matter for most Accumulators as they only emit a single scalar value where the cost of copying is pretty low. However, for ones that emit significant internal state (like count DISTINCT) using the same internal state can save a lot of copying (again, see #8849 for an example)

Also, the actual Accumulator instances are never used after a call to evaluate/state, so the state of the accumulator after this call is never used again.

Describe the solution you'd like

I would like to change Accumulator::evaluate and Accumulator::state to take &mut self

This is also consistent with GroupsAccumulator which takes mut for its state and evaluate functions:

pub trait GroupsAccumulator: Send {
...
    fn evaluate(
        &mut self,
        emit_to: EmitTo
    ) -> Result<Arc<dyn Array>, DataFusionError>;
    fn state(
        &mut self,
        emit_to: EmitTo
    ) -> Result<Vec<Arc<dyn Array>>, DataFusionError>;
...

Describe alternatives you've considered

No response

Additional context

No response