Atomic DROP TRIGGER

The purpose of this task is to ensure that DROP TRIGGER is atomic.

Description of how atomic drop trigger should work:

Logging of DROP TRIGGER

• Log to ddl log:
• db
• table name
• trigger name
• xid /* Used to check if query was already logged to binary log */
• initial length of the .TRG file
• query if there is space for it, if not log a zero length query.

Recovery operations:

• Delete if exists 'database/trigger_name.TRN~'
  If this file existed, it means that we crashed before the trigger
  was deleted and there is nothing else to do.
• Get length of TRG file
• If file length is unchanged, trigger was not dropped. Nothing else to do.
• Log original query to binary, if it was stored in the ddl log. If it was not stored (long query
  string), log the following query to binary log:
  use `database` ; DROP TRIGGER IF EXISTS `trigger_name` /* generated by ddl log */