### 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
var project = as(exchange.child(), ProjectExec.class);
        var extract = as(project.child(), FieldExtractExec.class);
        var source = as(extract.child(), EsQueryExec.class);
        assertThat(source.sorts().size(), equalTo(1));
        assertThat(source.sorts().get(0).field().name(), equalTo("job.raw"));
    }
    public void testFieldExtractForTextAndSubfield() {
        var plan = physicalPlan("""
            from test
            | keep job*
            """);
        var project = as(plan, ProjectExec.class);
        assertThat(Expressions.names(project.projections()), contains("job", "job.raw"));
    }
    public void testFieldExtractWithoutSourceAttributes() {
        PhysicalPlan verifiedPlan = optimizedPlan(physicalPlan("""
            from test
            | where round(emp_no) > 10
            """));
        
        List<Attribute> emptyAttrList = List.of();
        var badPlan = verifiedPlan.transformDown(
            EsQueryExec.class,
            node -> new EsSourceExec(node.source(), node.index(), emptyAttrList, node.query())
        );
        var e = expectThrows(PhysicalVerificationException.class, () -> physicalPlanOptimizer.verify(badPlan));
        assertThat(
            e.getMessage(),
            containsString(
                "Need to add field extractor for [[emp_no]] but cannot detect source attributes from node [EsSourceExec[test][]]"