executor, privilege: fix some two bug of RBAC

[imtbkcat]

What problem does this PR solve?

Fix two bug of RBAC.

bug 1: CURRENT_ROLE is not handle correctly in GRANT ROLE

mysql> create role r_1;
Query OK, 1 row affected (0.01 sec)

mysql> grant r_1 to current_user();
ERROR 1396 (HY000): Operation GRANT ROLE failed for @

bug 2: REVOKE ROLE doesn't delete information in mysql.default_role

mysql> REVOKE r1 FROM u1@localhost;
Query OK, 0 rows affected (0.01 sec)

mysql> select * from mysql.default_roles;
+-----------+------+-------------------+-------------------+
| HOST      | USER | DEFAULT_ROLE_HOST | DEFAULT_ROLE_USER |
+-----------+------+-------------------+-------------------+
| localhost | u1   | %                 | r1                |
+-----------+------+-------------------+-------------------+
1 row in set (0.00 sec)

What is changed and how it works?

1. Add check for CURRENT_USER in GrantRoleExec, if User is CURRENT_USER, it will be set to current user.
2. Delete information from mysql.default_role in RevokeRoleStmt.

Check List

Tests

• Unit test

Code changes

Side effects

• Increased code complexity

Related changes

• Need to cherry-pick to the release branch

[codecov]

Codecov Report

Merging #11273 into master will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master     #11273   +/-   ##
===========================================
  Coverage   81.2607%   81.2607%           
===========================================
  Files           423        423           
  Lines         90233      90233           
===========================================
  Hits          73324      73324           
  Misses        11607      11607           
  Partials       5302       5302

[imtbkcat]

/run-all-tests tidb-test=pr/847

[imtbkcat]

/run-common-test tidb-test=pr/847

[imtbkcat]

/run-common-test

[imtbkcat]

/run-all-tests

[tiancaiamao]

LGTM

[jackysp]

LGTM

[sre-bot]

cherry pick to release-3.0 in PR #11356