### 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/PhysicalPlanOptimizerTests.java
* _name{f}#11, salary{f}#12]]
     *       \_FieldExtractExec[_meta_field{f}#13, emp_no{f}#7, first_name{f}#8, ge..]
     *         \_EsQueryExec[test], query[][_doc{f}#16], limit[10000], sort[] estimatedRowSize[324]
     */
    public void testExtractorMultiEvalWithDifferentNames() {
        var plan = physicalPlan("""
            from test
            | eval e = emp_no + 1
            | eval emp_no = emp_no + 1
            """);
        var optimized = optimizedPlan(plan);
        var eval = as(optimized, EvalExec.class);
        var topLimit = as(eval.child(), LimitExec.class);
        var exchange = asRemoteExchange(topLimit.child());
        var project = as(exchange.child(), ProjectExec.class);
        var extract = as(project.child(), FieldExtractExec.class);
        assertThat(
            names(extract.attributesToExtract()),
            contains("_meta_field", "emp_no", "first_name", "gender", "job", "job.raw", "languages", "last_name", "long_noidx", "salary")
        );
    }
    /**
     * Expected
     * EvalExec[[emp_no{f}#7 + 1[INTEGER] AS emp_no, emp_no{r}#3 + 1[INTEGER] AS emp_no]]
     * \_LimitExec[10000[INTEGER]]
     *   \_ExchangeExec[[],false]
     *     \_ProjectExec[[_meta_field{f}#13, emp_no{f}#7, first_name{f}#8, gender{f}#9, job{f}#14, job.raw{f}#15, languages{f}#10, last
     * _name{f}#11, salary{f}#12]]
     *       \_FieldExtractExec[_meta_field{f}#13, emp_no{f}#7, first_name{f}#8, ge..]
     *         \_EsQueryExec[test], query[][_doc{f}#16], limit[10000], sort[] estimatedRowSize[324]