ddl: Partition duplicate name fix

[mjonss]

What problem does this PR solve?

Issue Number: close #31681

Problem Summary:
TRUNCATE PARTITION allows duplicate partition names in MySQL but not in TiDB (fixed by this PR)
DROP PARTITION could allow duplicate partition names in TiDB but not in MySQL (disallowed in TiDB by this PR)
(+ minor error handling more compatible with MySQL)

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

Better error compatibility with MySQL for TRUCATE/DROP PARTITION

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• hawkingrei
• tiancaiamao

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/d3aae7c9359ad9732341f2e87f7bf439ca619971

[tiancaiamao]

/merge

[ti-chi-bot]

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

Commit hash: c5b0fdb

[ti-chi-bot]

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