### 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
Order.OrderDirection.ASC,
                    Order.NullsPosition.LAST
                )
            )
        );
        assertThat(topN.child().collect(OrderBy.class::isInstance), is(emptyList()));
    }
    public void testPruneRedundantSortClauses() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | sort salary desc nulls last, emp_no desc nulls first
            | where salary > 2
            | eval e = emp_no * 2
            | keep salary, emp_no, e
            | sort e, emp_no desc, salary desc, emp_no desc nulls last""");
        var project = as(plan, Project.class);
        var topN = as(project.child(), TopN.class);
        assertThat(
            topN.order(),
            contains(
                new Order(
                    EMPTY,
                    new ReferenceAttribute(EMPTY, "e", INTEGER, null, Nullability.TRUE, null, false),
                    Order.OrderDirection.ASC,
                    Order.NullsPosition.LAST
                ),
                new Order(
                    EMPTY,
                    new FieldAttribute(EMPTY, "emp_no", mapping.get("emp_no")),
                    Order.OrderDirection.DESC,