### 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/main/java/org/elasticsearch/xpack/esql/optimizer/LogicalPlanOptimizer.java
protected In createIn(Expression key, List<Expression> values, ZoneId zoneId) {
            return new In(key.source(), key, values);
        }
        protected Equals createEquals(Expression k, Set<Expression> v, ZoneId finalZoneId) {
            return new Equals(k.source(), k, v.iterator().next(), finalZoneId);
        }
    }
    static class ReplaceLimitAndSortAsTopN extends OptimizerRules.OptimizerRule<Limit> {
        @Override
        protected LogicalPlan rule(Limit plan) {
            LogicalPlan p = plan;
            if (plan.child() instanceof OrderBy o) {
                p = new TopN(plan.source(), o.child(), o.order(), plan.limit());
            }
            return p;
        }
    }
    public static class ReplaceRegexMatch extends OptimizerRules.ReplaceRegexMatch {
        protected Expression regexToEquals(RegexMatch<?> regexMatch, Literal literal) {
            return new Equals(regexMatch.source(), regexMatch.field(), literal);
        }
    }
}