*: Make DDL unaffected by killing TiDB instance

[zimulala]

What problem does this PR solve?

Issue Number: close #43854

Problem Summary:

1. This issue support canceling DDL statements with KILL（related PR:*: fix a data race on TestConnExecutionTimeout #35923）.
   ---The original PR that supported this didn't seem to say cancel DDL on "kill TiDB"

2. But after these PRs, when we do kill TiDB, this TiDB's DDLs may be canceled(In some cases it can't be cancelled).
   --- Cancel DDL is not fully supported in the case of "kill TiDB".

3. This issue need do "Pause user DDL when upgrading TiDB", but these DDLs may be canceled by kill TiDB. So we consider kill TiDB can not cancel DDL.

4. We'll deal with this in detail when we distinguish between asynchronous and synchronous DDLs.

What is changed and how it works?

If don't we kill TiDB can't cancel DDLs.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Make DDL unaffected by the KILL TiDB command"

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lcwangchao
• tiancaiamao

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[zimulala]

PTAL @tiancaiamao

[zimulala]

/retest-required

[zimulala]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: a509ee1

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #43910.