statistics/handle: use StatementContext with TimeZone in initStatsBuckets4Chunk

[xuyifangreeneyes]

What problem does this PR solve?

Issue Number: close #41938

Problem Summary:

What is changed and how it works?

Use a newly-created StatementContext with UTC TimeZone when calling (*Datum).ConvertTo for upper/lower bounds in initStatsBuckets4Chunk.

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:

• Yisaer
• chrysan

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[xuyifangreeneyes]

/merge

[ti-chi-bot]

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

Commit hash: c5e6dac

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #42004.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.6: #42005.

[xuyifangreeneyes]

/cherry-pick release-6.5-20230425-v6.5.2

[ti-chi-bot]

@xuyifangreeneyes: new pull request created to branch release-6.5-20230425-v6.5.2: #43931.

In response to this:

/cherry-pick release-6.5-20230425-v6.5.2

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