### 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
assertTrue(or.left() instanceof LessThan);
        assertTrue(or.right() instanceof GreaterThan);
        var limit2 = as(filter.child(), Limit.class);
        assertTrue(limit2.child() instanceof EsRelation);
    }
    public void testPushDownFilterPastProject() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | rename emp_no as x
            | keep x
            | where x > 10""");
        var keep = as(plan, Project.class);
        var limit = as(keep.child(), Limit.class);
        var filter = as(limit.child(), Filter.class);
        var attr = filter.condition().collect(Attribute.class::isInstance).stream().findFirst().get();
        assertThat(as(attr, FieldAttribute.class).name(), is("emp_no"));
    }
    public void testPushDownEvalPastProject() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | rename emp_no as x
            | keep x
            | eval y = x * 2""");
        var keep = as(plan, Project.class);
        var eval = as(keep.child(), Eval.class);
        assertThat(
            eval.fields(),
            contains(
                new Alias(
                    EMPTY,