### 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
var filter = as(limit.child(), Filter.class);
        as(filter.condition(), IsNotNull.class);
        assertTrue(filter.child() instanceof EsRelation);
    }
    public void testSimplifyRLikeNoWildcard() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | where first_name rlike "foo"
            """);
        var limit = as(plan, Limit.class);
        var filter = as(limit.child(), Filter.class);
        assertTrue(filter.condition() instanceof Equals);
        Equals equals = as(filter.condition(), Equals.class);
        assertEquals(BytesRefs.toBytesRef("foo"), equals.right().fold());
        assertTrue(filter.child() instanceof EsRelation);
    }
    public void testSimplifyRLikeMatchAll() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | where first_name rlike ".*"
            """);
        var limit = as(plan, Limit.class);
        var filter = as(limit.child(), Filter.class);
        var isNotNull = as(filter.condition(), IsNotNull.class);
        assertTrue(filter.child() instanceof EsRelation);
    }
    public void testFoldNullInToLocalRelation() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | where null in (first_name, ".*")