Only return certain mysql errors from backend.
The following errors is returned as is from backend:
error code 1064 (parse error)
error code 1054 (bad column/field selected)
error code 1146 (table not exists)
Any other errors is logged and returned as a generic
error.
Restrict use of certain functions:
Do not allow usage of the following in query:
system_user()
session_user()
current_user() or current_user
user()
show grants
Fixes#19360
