* executor: implement memDelta for count funcs to track memUsage
* fix stdlib unsafe need be group together and before non-stdlib group in ../../executor/aggfuncs/func_count.go
* fix UpdatePartialResult memDelta return if err != nil
* fix
1 DefPartialResult4CountSize is the memory usage of AllocPartialResult, UpdatePartialResult will not use more memory, return 0, err.
2 in testcase TestMemCount count funcs are not distinct, use defaultUpdateMemDeltaGens and set isDistinct false
* fix UpdatePartialResult not use more memory
* fix MergePartialResult memDelta
Co-authored-by: ti-srebot <66930949+ti-srebot@users.noreply.github.com>
