HashAggregte: Aggregtor 与聚合算子实现

AggregateSinkOperator 的输入源通过 AggregateSinkOperator::push_chunk 完全输入到 Aggregator 后，构建好 HashMap 会通知 AggregateSourceOperator::pull_chunk 从 Aggregator 的 hashmap 提取chunk。

Aggregator

Aggregator 基于生成的 TAggregationNode 中包含的信息进行初始化：

struct TAggregationNode {
  1: optional list<Exprs.TExpr> grouping_exprs
  // aggregate exprs. The root of each expr is the aggregate function. 
  // The other exprs are the inputs to the aggregate function.
  2: required list<Exprs.TExpr> aggregate_functions

  // Tuple id used for intermediate aggregations 
  // (with slots of agg intermediate types)
  3: required Types.TTupleId intermediate_tuple_id

  // Tupld id used for the aggregation output (with slots of agg output types)
  // Equal to intermediate_tuple_id if intermediate type == output type for all
  // aggregate functions.
  4: required Types.TTupleId output_tuple_id

  // Set to true if this aggregation function requires finalization to complete
  // after all rows have been aggregated, and this node is not an intermediate
  5: required bool need_finalize
  6: optional bool use_streaming_preaggregation

  // For vector query engine
  20: optional bool has_outer_join_child
  21: optional TStreamingPreaggregationMode streaming_preaggregation_mode

  // For profile attributes' printing: `Grouping Keys` `Aggregate Functions`
  22: optional string sql_grouping_keys
  23: optional string sql_aggregate_functions

  24: optional i32 agg_func_set_version = 1
  
  // used in query cache
  25: optional list<Exprs.TExpr> intermediate_aggr_exprs

  // used in pipeline engine
  26: optional bool interpolate_passthrough = false
  
  27: optional bool use_sort_agg
}