### 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/test/java/org/elasticsearch/xpack/esql/optimizer/LogicalPlanOptimizerTests.java
| sort emp_no
            | where emp_no > 10
            | sort salary""");
        var topN = as(plan, TopN.class);
        assertThat(orderNames(topN), contains("salary", "emp_no"));
        var filter = as(topN.child(), Filter.class);
        as(filter.child(), EsRelation.class);
    }
    private static List<String> orderNames(TopN topN) {
        return topN.order().stream().map(o -> as(o.child(), NamedExpression.class).name()).toList();
    }
    public void testCombineLimitWithOrderByThroughFilterAndEval() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | sort salary
            | eval x = emp_no / 2
            | where x > 20
            | sort x
            | limit 10""");
        var topN = as(plan, TopN.class);
        var filter = as(topN.child(), Filter.class);
        var eval = as(filter.child(), Eval.class);
        as(eval.child(), EsRelation.class);
    }
    public void testCombineMultipleOrderByAndLimits() {