Aggregate Functions Restored to Case Sensitivity in ClickHouse

Aggregate functions boundingRatio, rankCorr, retention, timeSeriesGroupSum, timeSeriesGroupRateSum, windowFunnel were erroneously made case-insensitive. Now their names are made case sensitive as designed. Only functions that are specified in SQL standard or made for compatibility with other DBMS or functions similar to those should be case-insensitive. #16407 (alexey-milovidov).