cherry-pick two commits (pingcap#27253)

planner: Fix the problem that `PlanBuilder.buildWindowFunctions` may …

…change sub operator's schema. (pingcap#27176)

statistics: fix the panic when analyze with collation enabled (pingca…

…p#21262) (pingcap#21299) (pingcap#26965)

Co-authored-by: ti-srebot <[email protected]>

executor: fix `shutdown` and `trace` statement audit log (pingcap#26936)

executor: fix `shutdown` and `trace` statement audit log (pingcap#26936)

executor: fix some audit log error (pingcap#26749)

store/tikv: increase batch split region limit (pingcap#24508) (pingca…

…p#26656)

expression: Fix wrong charset and collation for case when function (p…

…ingcap#26663) (pingcap#26675)

tikvclient: add more logs to debug (pingcap#26664)

* add logs

planner: the UNION's merge type should exclude the pure NULL (pingcap…

…#26561) (pingcap#26570)