WL#10922: Remove global scope sql_log_bin system variable

Affects: Server-8.x   —   Status: Complete   —   Priority: Medium

EXECUTIVE SUMMARY
=================

global.sql_log_bin was set read only in MySQL 5.5, 5.6 and 5.7.  In
addition, reading this variable was deprecated in MySQL 5.7. This
patch removes the global scope of sql_log_bin system variable in MySQL
8.0.

Notes
=====

Item deprecated by

  BUG#67433: USING SET GLOBAL SQL_LOG_BIN SHOULD NOT BE ALLOWED:

  * global scope for sql_log_bin should be removed completely (5.7
    made it read only with a warning)

This task is to remove the global scope for the sql_log_bin system
variable in 8.0.
FR1. When issuing SELECT @@global.sql_log_bin shall return error
     ER_INCORRECT_GLOBAL_LOCAL_VAR

FR2. When issuing SET @@global.sql_log_bin SHALL return error
     ER_LOCAL_VARIABLE
User Visible Changes
====================

- SELECT @@global.sql_log_bin now results in an error, instead of a
  deprecation warning and a value. The error returned is: 

  ER_INCORRECT_GLOBAL_LOCAL_VAR

  Example:

  mysql> SELECT @@global.sql_log_bin;
  ERROR 1238 (HY000): Variable 'sql_log_bin' is a SESSION variable


- SET @@global.sql_log_bin=1 now results in a different
  error. Previously, it returned ER_WRONG_VALUE_FOR_VAR, now it
  returns ER_LOCAL_VARIABLE

  Example:

  mysql> SET @@global.sql_log_bin=1;
  ERROR 1228 (HY000): Variable 'sql_log_bin' is a SESSION variable and can't be
used with SET GLOBAL

Upgrades
========

After upgrading, users that had tooling or scripts written relying on
the (deprecated) behavior of SELECT @@global.sql_log_bin will stop
working.

Security
========

There are no security considerations. In fact, the access to
sql_log_bin has been restricted on a per session basis. This means
that sql_log_bin global value cannot be exposed through concurrent
sessions.
LOW LEVEL CHANGES
=================

1. Adjust the MTR test cases that read the global var of sql_log_bin.

2. Remove the code to emit the deprecation warning in sys_vars.cc.

3. Remove the class Session_var_sql_log_bin which can now be reverted
   back to a vanilla Sql_log_bool class.

4. Remove special case for global sql_log_bin on storage/perfschema/pfs_variable.cc