Fix cast to decimal overflow bug (#3922)

[ti-chi-bot]

This is an automated cherry-pick of #3922

What problem does this PR solve?

Issue Number: close #3920

Problem Summary: todo

What is changed and how it works?

1. DAGContext.h/.cpp: expose TiDBSQLFLags so we can use it in unittest(TIDBSQLFlags::OVERFLOW_AS_WARNING). Also fix one clang-tidy.
2. FunctionsTiDBConversion.h: fix the logic that check if overflow happens or not. We should compare inner_value with inner_max_value or out_value with outer_max_value. I choose inner_value here.
3. gtest_tidb_conversion.cpp: add unit test when overflow happens.

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

Fix cast to decimal overflow bug

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• SeaRise
• mengxin9014

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[guo-shaoge]

/run-all-tests

[guo-shaoge]

/run-all-tests

[guo-shaoge]

/merge

[ti-chi-bot]

@guo-shaoge: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

You only need to trigger /merge once, and if the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

If you have any questions about the PR merge process, please refer to pr process.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

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

Commit hash: 9142071

[ti-chi-bot]

@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[guo-shaoge]

/run-integration-test