Expressions should also evaluate on statistics

[rdettai]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Physical expressions should be aware of the rules on how to propagate statistics. For instance, for the row-wise max of two columns, the maximum statistics is the greatest of the maximum of the two input input columns. This would allow the ProjectionExec node to provide much better statistics.

Describe the solution you'd like
We should extend the PhysicalExpr trait with a method that handles statistics:

fn stats_eval(&self, stats: &Statitistics) -> Result<Statistics>

Describe alternatives you've considered
This could be implemented in the ProjectionExec with downcasting on various expression types.

Additional context
This is a follow up of #962

[Dandandan]

That's a great idea 👍

[alamb]

with #1070, this feature could replace the existing partition pruning logic with a more general purpose implementation. 👍

[alamb]

I think PhysicalExpr.html::evaluate_bounds https://docs.rs/datafusion/latest/datafusion/physical_expr/trait.PhysicalExpr.html#method.evaluate_bounds

Implements this partly (though it is in terms of bounds, not statistics) 🤔