### Description

Evals that introduce aliased can be simplified by extracting them into a project (and thus signaling there's no underlying processing).

The following eval:
`eval x = a + 1, y = x, z = y + 1, y = z, w = y + 1`
can be converted into:
`eval x = a + 1, z = a + 1 + 1, w = a + 1 + 1 | project x, z, z as y, w`

This helps fuse the project with other projections/aggs downstream.
x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/LogicalPlanOptimizer.java
CombineEvals() {
            super(TransformDirection.UP);
        }
        @Override
        protected LogicalPlan rule(Eval eval) {
            LogicalPlan plan = eval;
            if (eval.child() instanceof Eval subEval) {
                plan = new Eval(eval.source(), subEval.child(), CollectionUtils.combine(subEval.fields(), eval.fields()));
            }
            return plan;
        }
    }
    
    
    
    
    static class PropagateEvalFoldables extends Rule<LogicalPlan, LogicalPlan> {