types: fix fsp for datetime, time and timestamp (#27170)

[ti-srebot]

cherry-pick #27170 to release-5.2
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/27243

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git push [email protected]:ti-srebot/tidb.git pr/27243:release-5.2-5ae87cae85ed

---

Signed-off-by: wjhuang2016 [email protected]

What problem does this PR solve?

Issue Number: close #27159

Problem Summary:
If the decimal is unspecified, we should use the maxFsp, which is compatible with what we do for function.

What is changed and how it works?

If the decimal is unspecified, we should use the maxFsp, which is compatible with what we do for function.

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

 'None' 

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• AilinKid
• tangenta

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[ti-srebot]

/run-all-tests

[ti-srebot]

@wjhuang2016 you're already a collaborator in bot's repo.

[AilinKid]

LGTM

[wjhuang2016]

/merge

[ti-chi-bot]

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

Commit hash: 52e32f9

[ti-chi-bot]

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[wjhuang2016]

/run-check_dev