*: add a column describing memory usage for table information_schema.processlist

[SunRunAway]

What problem does this PR solve?

Closes #10199

What is changed and how it works?

Add a column describing memory usage for table information_schema.processlist and keep show processlist acting as before.

mysql> SELECT * FROM information_schema.processlist;
+------+------+-----------+------+---------+------+-------+----------------------------------------------+------+
| ID   | USER | HOST      | DB   | COMMAND | TIME | STATE | INFO                                         | MEM  |
+------+------+-----------+------+---------+------+-------+----------------------------------------------+------+
|    1 | root | 127.0.0.1 | test | Query   |    1 | 2     | select * from t, ta                          |  856 |
|    2 | root | 127.0.0.1 | test | Query   |    0 | 2     | SELECT * FROM information_schema.processlist |    0 |
+------+------+-----------+------+---------+------+-------+----------------------------------------------+------+
2 rows in set (0.00 sec)

mysql> show processlist;
+------+------+-----------+------+---------+------+-------+----------------------+
| Id   | User | Host      | db   | Command | Time | State | Info                 |
+------+------+-----------+------+---------+------+-------+----------------------+
|    2 | root | 127.0.0.1 | test | Query   |    0 | 2     | show processlist     |
|    1 | root | 127.0.0.1 | test | Query   |    1 | 2     | select *  from t, ta |
+------+------+-----------+------+---------+------+-------+----------------------+
2 rows in set (0.01 sec)

Check List

Tests

• Unit test
• Manual test (see above)

Code changes

• Has exported function/method change

Side effects

• Increased code complexity

Related changes

• Need to update the documentation
• Need to be included in the release note?

---

This change is 

[codecov]

Codecov Report

Merging #10837 into master will increase coverage by 0.0173%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##            master     #10837        +/-   ##
===============================================
+ Coverage   80.863%   80.8804%   +0.0174%     
===============================================
  Files          419        419                
  Lines        88661      88658         -3     
===============================================
+ Hits         71694      71707        +13     
+ Misses       11738      11725        -13     
+ Partials      5229       5226         -3

[SunRunAway]

@zz-jason @XuHuaiyu PTAL

[XuHuaiyu]

LGTM

[SunRunAway]

@XuHuaiyu sorry, PTAL again.

[XuHuaiyu]

LGTM

[zz-jason]

LGTM

[zz-jason]

/run-all-tests

[SunRunAway]

/rebuild