### 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 org.elasticsearch.xpack.ql.plan.logical.LogicalPlan;
import org.elasticsearch.xpack.ql.plan.logical.OrderBy;
import org.elasticsearch.xpack.ql.plan.logical.Project;
import org.elasticsearch.xpack.ql.tree.Source;
import org.elasticsearch.xpack.ql.type.DataType;
import org.elasticsearch.xpack.ql.type.DataTypes;
import org.elasticsearch.xpack.ql.type.EsField;
import org.junit.BeforeClass;
import java.util.List;
import java.util.Map;
import java.util.Set;
import static java.util.Collections.emptyList;
import static java.util.Collections.emptyMap;
import static java.util.Collections.singletonList;
import static org.elasticsearch.xpack.esql.EsqlTestUtils.L;
import static org.elasticsearch.xpack.esql.EsqlTestUtils.TEST_VERIFIER;
import static org.elasticsearch.xpack.esql.EsqlTestUtils.as;
import static org.elasticsearch.xpack.esql.EsqlTestUtils.emptySource;
import static org.elasticsearch.xpack.esql.EsqlTestUtils.loadMapping;
import static org.elasticsearch.xpack.esql.EsqlTestUtils.localSource;
import static org.elasticsearch.xpack.ql.TestUtils.relation;
import static org.elasticsearch.xpack.ql.tree.Source.EMPTY;
import static org.elasticsearch.xpack.ql.type.DataTypes.INTEGER;
import static org.hamcrest.Matchers.contains;
import static org.hamcrest.Matchers.containsString;
import static org.hamcrest.Matchers.empty;
import static org.hamcrest.Matchers.emptyArray;
import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.Matchers.hasSize;
import static org.hamcrest.Matchers.instanceOf;