[TD-4910]fix double free issue

[TD-4915]<fix> fix show create database except

[td-4905]<fix>:fix import caused crash.

Docs/update latest feature

1. rename semphone to semaphore
2. add comment for tsched.h
3. change the function signature for taosSchedulerTask, changing from
return int to void. We currently don't check any return code of the function.
4. add some error handlings. For fatal error, just exit the process because
the program may run into a random state.

[TD-4926]<fix>:fix core during operator time usage calculate

* fix crash if no result file.

* make taosdemo same as master branch.

[TD-4756]<fix>: nanosecond precison on gcBuildQueryJson

[TD-4561]feature:support statistics about operators running time

Feature/query

[TD-4879]fix mem leak issue

[TD-4098]<fix> unsigned date type not found

Docs/update latest feature

add test case to verify taosdump with binary and nchar data

add test case to verify taosdump with binary and nchar data