### 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
            | dissect first_name "%{x}"
            | sort x""");
        var topN = as(plan, TopN.class);
        assertThat(orderNames(topN), contains("x", "emp_no"));
        var dissect = as(topN.child(), Dissect.class);
        as(dissect.child(), EsRelation.class);
    }
    public void testCombineOrderByThroughGrok() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | sort emp_no
            | grok first_name "%{WORD:x}"
            | sort x""");
        var topN = as(plan, TopN.class);
        assertThat(orderNames(topN), contains("x", "emp_no"));
        var grok = as(topN.child(), Grok.class);
        as(grok.child(), EsRelation.class);
    }
    public void testCombineOrderByThroughProject() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | sort emp_no
            | keep salary, emp_no
            | sort salary""");
        var keep = as(plan, Project.class);
        var topN = as(keep.child(), TopN.class);
        assertThat(orderNames(topN), contains("salary", "emp_no"));
        as(topN.child(), EsRelation.class);
    }