Function bind_aggregate_calls 

pub fn bind_aggregate_calls(
    expr: &Expr,
    projection: &[SelectItem],
    aggregates: &mut Vec<AggregateExpr>,
    functions: &FunctionRegistry,
    name: BindName,
    scope: &TableScope,
) -> Result<Expr>

Rewrite every aggregate call in expr to a reference to its computed column, registering aggregates the projection did not already request.

scope carries the input relations each aggregate argument resolves against.