grants are reapplied.


After renaming a user and trying to re-apply grants results in additional
grants.

This is because we use username as part of the key for GRANT_TABLE structure.
When the user is renamed, we only change the username stored and the hash key
still contains the old user name and this results in the extra privileges

Fixed by rebuilding the hash key and updating the column_priv_hash structure
when the user is renamed

mysql-test/r/grant3.result:
  Bug #41597 - After rename of user, there are additional grants when 
               grants are reapplied.
  
  Testcase for BUG#41597
mysql-test/t/grant3.test:
  Bug #41597 - After rename of user, there are additional grants when 
               grants are reapplied.
  
  Testcase for BUG#41597
sql/sql_acl.cc:
  Bug #41597 - After rename of user, there are additional grants when 
               grants are reapplied.
  
  Fixed handle_grant_struct() to update the hash key when the user is renamed.
  Added to set_user_details() method to GRANT_NAME class