Release savepoint is incompatible with mysql

[zyguan]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

/* test */ select version();
/* test */ drop table if exists t;
/* test */ create table t (k int primary key, v varchar(20));
/* test */ begin;
/* test */ insert into t values (1, 'a');
/* test */ savepoint p1;
/* test */ insert into t values (2, 'b');
/* test */ savepoint p2;
/* test */ release savepoint p1;
/* test */ rollback to p2; -- tidb: OK; mysql: SAVEPOINT p2 does not exist
/* test */ rollback;

2. What did you expect to see? (Required)

The result of rollback to p2 should be consistent with mysql

3. What did you see instead (Required)

tidb returned ok, however mysql reported an error.

4. What is your TiDB version? (Required)

master

[zyguan]

duplicated with #35063