Tidb: Potential timezone related bugs caused by `gotime.Local` location

[bb7133]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   When dealing with timestamps, currently there are several pieces of codes that used gotime.Local as the timezone location rather than system/global/session variables, which may lead to unexpected errors:

• https://github.com/pingcap/tidb/blob/61f24d246995ceb6181da779c934c9a05438c3a9/types/mytime.go#L79

• https://github.com/pingcap/tidb/blob/61f24d246995ceb6181da779c934c9a05438c3a9/types/time.go#L433

• ...

  For example, #13605 is a bug caused by such codes, we should try to avoid using gotime.Local to prevent such errors.

1. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?
   Such codes exist in all TiDB versions.

[hi-rustin]

I am working on it.

[bb7133]

Thanks! @Rustin-Liu

[fzhedu]

@bb7133 can we close this issue?

[hi-rustin]

I remember it seems that we still have this problem in some places. So maybe we can find all the problems and open a new issue to track them.

Or just keep this and update the issue desc? @fzhedu cc: @bb7133