### 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/PhysicalPlanOptimizerTests.java
var project = as(exchange.child(), ProjectExec.class);
        var extract = as(project.child(), FieldExtractExec.class);
        var limit2 = as(extract.child(), LimitExec.class);
        var filter = as(limit2.child(), FilterExec.class);
        var extract2 = as(filter.child(), FieldExtractExec.class);
        var source = source(extract2.child());
        assertNull(source.query());
    }
    public void testTextWithRawFilterPushDown() {
        var plan = physicalPlan("""
            from test
            | where job == "foo"
            """);
        var optimized = optimizedPlan(plan);
        var limit = as(optimized, LimitExec.class);
        var exchange = asRemoteExchange(limit.child());
        var project = as(exchange.child(), ProjectExec.class);
        var extract = as(project.child(), FieldExtractExec.class);
        var source = as(extract.child(), EsQueryExec.class);
        var qb = as(source.query(), SingleValueQuery.Builder.class);
        assertThat(qb.field(), equalTo("job.raw"));
    }
    public void testNoTextSortPushDown() {
        var plan = physicalPlan("""
            from test
            | sort gender
            """);
        var optimized = optimizedPlan(plan);
        var topN = as(optimized, TopNExec.class);
        var exchange = as(topN.child(), ExchangeExec.class);