### 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
LessThan conditionB = lessThanOf(getFieldAttribute("b"), TWO);
        Filter fa = new Filter(EMPTY, relation, conditionA);
        List<FieldAttribute> projections = singletonList(getFieldAttribute("b"));
        EsqlProject keep = new EsqlProject(EMPTY, fa, projections);
        Filter fb = new Filter(EMPTY, keep, conditionB);
        Filter combinedFilter = new Filter(EMPTY, relation, new And(EMPTY, conditionA, conditionB));
        assertEquals(new EsqlProject(EMPTY, combinedFilter, projections), new LogicalPlanOptimizer.PushDownAndCombineFilters().apply(fb));
    }
    public void testPushDownLikeRlikeFilter() {
        EsRelation relation = relation();
        org.elasticsearch.xpack.ql.expression.predicate.regex.RLike conditionA = rlike(getFieldAttribute("a"), "foo");
        WildcardLike conditionB = wildcardLike(getFieldAttribute("b"), "bar");
        Filter fa = new Filter(EMPTY, relation, conditionA);
        List<FieldAttribute> projections = singletonList(getFieldAttribute("b"));
        EsqlProject keep = new EsqlProject(EMPTY, fa, projections);
        Filter fb = new Filter(EMPTY, keep, conditionB);
        Filter combinedFilter = new Filter(EMPTY, relation, new And(EMPTY, conditionA, conditionB));
        assertEquals(new EsqlProject(EMPTY, combinedFilter, projections), new LogicalPlanOptimizer.PushDownAndCombineFilters().apply(fb));
    }
    
    
    public void testSelectivelyPushDownFilterPastFunctionAgg() {
        EsRelation relation = relation();
        GreaterThan conditionA = greaterThanOf(getFieldAttribute("a"), ONE);
        LessThan conditionB = lessThanOf(getFieldAttribute("b"), TWO);
        GreaterThanOrEqual aggregateCondition = greaterThanOrEqualOf(new Count(EMPTY, ONE), THREE);
        Filter fa = new Filter(EMPTY, relation, conditionA);
        
        Aggregate aggregate = new Aggregate(EMPTY, fa, singletonList(getFieldAttribute("b")), emptyList());
        Filter fb = new Filter(EMPTY, aggregate, new And(EMPTY, aggregateCondition, conditionB));