[ES|QL] Substitue date_trunc with round_to when the pre-calculated rounding points are available

[fang-xing-esql]

This is a subtask of the filter-by-filter aggregation in ES|QL. And the following changes are included in this PR.

• Consolidated min/max per shard into SearchStats, according to the statistics retrieved from Lucent for DateFieldType only, added SearchContextStatsTests, and tested min/max.
• At date nodes, if min/max are available in SearchStats, provide them to DateTrunc.createRounding, call prepare(min, max), instead of prepareForUnknown().
• At data node, pre-calculated rounding points are returned by fixedRoundingPoints(), substitute date_trunc and bucket with round_to function. A new rule SubstituteSurrogateExpressionsWithSearchStats is added in the local rewrite batch in LocalLogicalPlanOptimizer to do the substitution.
• The rewrite from date_trunc/bucket to round_to does not apply to date_nanos yet, as the underlying APIs support millis only, and nanos has not been tested yet.
• PreparedRounding.maybeUseArray may hit an assert if the calendar intervals are multiple quantities, like 10 month or 3 quarter, date histogram aggregation has this limitation documented here,this is likely why the assert hasn't been hit before, and the same limitation will apply to this rewrite.

Next step: performance validations.

[elasticsearchmachine]

Hi @fang-xing-esql, I've created a changelog YAML for you.