ddl, tests: add expression default values feature relevant tests for some DDLs and fix a related bug (#51571)

[ti-chi-bot]

This is an automated cherry-pick of #51571

What problem does this PR solve?

Issue Number: close #51554, close #51570

Problem Summary:

What changed and how does it work?

• Add expression default values feature relevant tests for "modify column", "set/drop default" and "add index"
• When the default value is an expression, changing it to a constant by "set default" can be problematic

Check List

Tests

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

  • I checked and no code files have been changed.

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

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-7.1@425cda9). Click here to learn what that means.
The diff coverage is 100.0000%.

Additional details and impacted files

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Defined2014, tangenta

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• OWNERS [Defined2014,tangenta]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-04-15 13:06:06.105940687 +0000 UTC m=+256985.216987137: ☑️ agreed by Defined2014.
• 2024-04-16 03:02:40.781481007 +0000 UTC m=+307179.892527451: ☑️ agreed by tangenta.