Migrate aggregation functions to function-v2

[RinChanNOWWW]

Summary

• combinator distinct. chore(query): migrate agg (count, sum, avg) and combinators into v2 #7615
• combinator if. chore(query): migrate agg (count, sum, avg) and combinators into v2 #7615
• count. chore(query): migrate agg (count, sum, avg) and combinators into v2 #7615
• sum. chore(query): migrate agg (count, sum, avg) and combinators into v2 #7615
• avg. chore(query): migrate agg (count, sum, avg) and combinators into v2 #7615
• uniq. chore(query): migrate agg (count, sum, avg) and combinators into v2 #7615
• min, max, any. feat(query): migrate min/max/any functions to v2. #7787
• arg_min, arg_max. feat(query): migrate agg functions arg_min and arg_max to v2. #7901
• std, stddev, stddev_pop feat(query): migrate agg function: stddev, window_funnel to func-v2 #8034
• covar_pop, covar_samp. feat(query): migrate aggregation covariance functions to v2. #7926
• window_funnel feat(query): migrate agg function: stddev, window_funnel to func-v2 #8034
• retention. feat(query): migrate retention to v2. #7952

something may be helpful

• add try_downcast_builder for ValueType. feat(query): add try_downcast_builder for ValueType. #7838
• unit tests for group by. feat(query): add unit tests for group by. #7845
• add Default for ValueType::Scalar or add default_scalar for ValueType.

[RinChanNOWWW]

• add Default for ValueType::Scalar or add default_scalar for ValueType.
• add try_downcast_builder for ValueType.

Are these necessary? cc @sundy-li

[RinChanNOWWW]

The Default bound seems not necessary, and not suitable for AnyType. Let's not consider this.

[TCeason]

stddev and Window funnel assign to @TCeason