ddl: fix add index on timestamp column bug

[crazycs520]

What problem does this PR solve?

reproduce SQL:

 drop table if exists t1;
 CREATE TABLE t1 (c2 YEAR, PRIMARY KEY (c2));
 INSERT INTO t1 SET c2 = '1912';
 ALTER TABLE t1 ADD COLUMN c3 TIMESTAMP NULL DEFAULT '1976-08-29 16:28:11';
 ALTER TABLE t1 ADD INDEX c5 (c2, c3);
 admin check table t1;

In old TiDB version, the SQL: admin check table t1 will return error cause by wrong index record.

What is changed and how it works?

In back fill record to index, if use the column default value, and if the column type is timestamp, We should convert the default timestamp value to UTC timestamp value.

Check List

Tests

• Unit test

Code changes

• Has exported function/method change

Related changes

• Need to cherry-pick to the release branch ?

[crazycs520]

@winkyao @ciscoxll PTAL

[shenli]

/run-all-tests

[jackysp]

LGTM

[ciscoxll]

LGTM.

Only two currently

[coocood]

LGTM

[sre-bot]

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