### 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
from test
            | eval y = emp_no + 1
            | rename y as 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, ReferenceAttribute.class).name(), is("y"));
        var eval = as(filter.child(), Eval.class);
        as(eval.child(), EsRelation.class);
    }
    public void testPushDownFilterPastProjectUsingDissect() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | dissect first_name "%{y}"
            | rename y as x
            | keep x
            | where x == "foo"
            """);
        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, ReferenceAttribute.class).name(), is("y"));
        var dissect = as(filter.child(), Dissect.class);
        as(dissect.child(), EsRelation.class);
    }
    public void testPushDownFilterPastProjectUsingGrok() {
        LogicalPlan plan = optimizedPlan("""