### 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
import static org.hamcrest.Matchers.is;
import static org.hamcrest.Matchers.startsWith;
public class LogicalPlanOptimizerTests extends ESTestCase {
    private static final Literal ONE = L(1);
    private static final Literal TWO = L(2);
    private static final Literal THREE = L(3);
    private static EsqlParser parser;
    private static Analyzer analyzer;
    private static LogicalPlanOptimizer logicalOptimizer;
    private static Map<String, EsField> mapping;
    @BeforeClass
    public static void init() {
        parser = new EsqlParser();
        mapping = loadMapping("mapping-basic.json");
        EsIndex test = new EsIndex("test", mapping);
        IndexResolution getIndexResult = IndexResolution.valid(test);
        logicalOptimizer = new LogicalPlanOptimizer();
        EnrichPolicyResolution policy = AnalyzerTestUtils.loadEnrichPolicyResolution(
            "languages_idx",
            "id",
            "languages_idx",
            "mapping-languages.json"
        );
        analyzer = new Analyzer(
            new AnalyzerContext(
                EsqlTestUtils.TEST_CFG,
                new EsqlFunctionRegistry(),
                getIndexResult,
                new EnrichResolution(Set.of(policy), Set.of("languages_idx", "something"))
            ),