statistics: fix the error that init stats might got failure when decoding column bucket (#55685)

[ti-chi-bot]

This is an automated cherry-pick of #55685

…

What problem does this PR solve?

Issue Number: close #55684

Problem Summary:

What changed and how does it work?

The old init stats doesn't handle the collation string.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

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]

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Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/check_dev_2	15b1c91	link	true	/test check-dev2

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[codecov]

Codecov Report

Attention: Patch coverage is 31.25000% with 22 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.1@92acec0). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.1     #56027   +/-   ##
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  Coverage               ?   71.1781%           
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  Files                  ?       1466           
  Lines                  ?     423110           
  Branches               ?          0           
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  Hits                   ?     301162           
  Misses                 ?     101421           
  Partials               ?      20527           

Flag	Coverage Δ
unit	71.1781% <31.2500%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.9656% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	41.3485% <0.0000%> (?)