privilege/privileges: refactor the data struct for user privilege data

[CbcWestwolf]

What problem does this PR solve?

Issue Number: ref #61706

Problem Summary:

What changed and how does it work?

Pick #58945

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

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.35938% with 17 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.5-20250606-v8.5.2@76ea2f2). Learn more about missing BASE report.

Additional details and impacted files

@@                       Coverage Diff                        @@
##             release-8.5-20250606-v8.5.2     #61719   +/-   ##
================================================================
  Coverage                               ?   57.5659%           
================================================================
  Files                                  ?       1770           
  Lines                                  ?     629518           
  Branches                               ?          0           
================================================================
  Hits                                   ?     362388           
  Misses                                 ?     242586           
  Partials                               ?      24544           

Flag	Coverage Δ
integration	38.0640% <89.8437%> (?)
unit	72.6866% <84.3750%> (?)

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

Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	63.1635% <0.0000%> (?)

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[CbcWestwolf]

/retest

[CbcWestwolf]

/retest

[CbcWestwolf]

/retest

[CbcWestwolf]

/retest

[CbcWestwolf]

/unhold

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: tiancaiamao, wjhuang2016

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• ~~OWNERS~~ [tiancaiamao,wjhuang2016]
• ~~pkg/ddl/OWNERS~~ [wjhuang2016]

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[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2025-07-01 11:49:38.213337205 +0000 UTC m=+1395630.936516173: :ballot_box_with_check: agreed by wjhuang2016.
• 2025-07-02 02:30:39.268255918 +0000 UTC m=+1448491.991434899: :ballot_box_with_check: agreed by tiancaiamao.