ddl: properly handle existence checks for deleted records in temp index

[Benjamin2037]

What problem does this PR solve?

Issue Number: close #39321

Problem Summary:
When set fast reorg variable on, some ut will failed.

What is changed and how it works?

TestCreateUniqueExpressionIndex

When user issue insert on dulplicate update statement during add index processing.

1. During insert on dulplicate update, it need check unique key exists. when this check processing is in fast_reorg add index period, the check key exists should be done on temp index.
2. Also the deleted key in temp index is not real delete, it is marked delete. So if this key was return, it should be skiped.
3. When user insert one row in unique index, we also need check if there is marked deleted key exist, if this deleted key exist, then we skip unique conflict check and then let insert could be successful.

TestIndexChange

This case has some trick place, it test different adding index schema stage to see if key is exist or not. But here still has above problem. In non-public status index, all changes on table that is adding index will reflect to temp idx.
So we have to change key exist also on temp index first.

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.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• tangenta
• wjhuang2016

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[Benjamin2037]

/run-mysql-test

[Benjamin2037]

/run-build

[Benjamin2037]

/run-mysql-test

[Benjamin2037]

/merge

[ti-chi-bot]

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

Commit hash: a16e7eb

[Benjamin2037]

/merge

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! New failing [1] after this pr merged.
These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/sqllogic-test-2	🟥 failed 1, success 27, total 28	8 min 43 sec	New failing
idc-jenkins-ci-tidb/integration-ddl-test	✅ all 6 tests passed	7 min 33 sec	Fixed
idc-jenkins-ci-tidb/integration-common-test	🟢 all 17 tests passed	27 min	Existing passed
idc-jenkins-ci/integration-cdc-test	🟢 all 40 tests passed	20 min	Existing passed
idc-jenkins-ci-tidb/common-test	🟢 all 11 tests passed	18 min	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	6 min 46 sec	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	6 min 24 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	6 min 11 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	3 min 12 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed