partition: fix split and scatter region for truncate partition (#43271)

[ti-chi-bot]

This is an automated cherry-pick of #43271

What problem does this PR solve?

Issue Number: close #43174 close #43028

Problem Summary:

What is changed and how it works?

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:

• Defined2014
• mjonss

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[mjonss]

/merge

[ti-chi-bot]

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

Commit hash: 8b498d1

[mjonss]

/retest

[mjonss]

/merge

[ti-chi-bot]

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

Commit hash: d8ab44a

[mjonss]

/retest

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

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