Add some debug info when meet duplicate key in parallel prehandling

[CalvinNeo]

What problem does this PR solve?

Issue Number: close #8081

Problem Summary:

it is reported that in some case, there are duplicated keys when merge uncommitted region data.
Add some debug info to peek exactly which key is duplicated.

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

None

[JaySon-Huang]

LGTM with minor comment

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hongyunyan, JaySon-Huang

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-10-11 06:53:16.023901414 +0000 UTC m=+1207993.611011559: ☑️ agreed by JaySon-Huang.
• 2023-10-11 07:04:22.773957897 +0000 UTC m=+1208660.361068041: ☑️ agreed by hongyunyan.

[CalvinNeo]

/run-all-tests

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