statistics: move JSON* to statistics/util

[winoros]

What problem does this PR solve?

Issue Number: ref #57949

Problem Summary:

To solve the cyclic import problem during refactoring statistics.Column and statistics.Index, we need to move the objects into a new place.

What changed and how does it work?

To make MemoryUsage safe to be o(1). We need to make sure the Column/Index not changed by accident.

This pr is one step of make the important fields of them private.

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]

Codecov Report

Attention: Patch coverage is 98.30508% with 1 line in your changes missing coverage. Please review.

Project coverage is 75.1476%. Comparing base (edba7e9) to head (43438c7).
Report is 11 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #57950        +/-   ##
================================================
+ Coverage   73.1804%   75.1476%   +1.9671%     
================================================
  Files          1671       1719        +48     
  Lines        460724     471243     +10519     
================================================
+ Hits         337160     354128     +16968     
+ Misses       102835      95048      -7787     
- Partials      20729      22067      +1338     

Flag	Coverage Δ
integration	49.2605% <18.6440%> (?)
unit	72.5822% <98.3050%> (+0.2625%)	⬆️

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

Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	61.6349% <ø> (+15.6486%)	⬆️

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-12-03 15:33:04.045470032 +0000 UTC m=+1168971.665124542: ☑️ agreed by tangenta.
• 2024-12-04 01:32:16.383623439 +0000 UTC m=+1204924.003277955: ☑️ agreed by Leavrth.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, Leavrth, tangenta

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Needs approval from an approver in each of these files:

• OWNERS [Leavrth,hawkingrei,tangenta]
• br/OWNERS [Leavrth]
• pkg/domain/OWNERS [tangenta]
• pkg/planner/OWNERS [hawkingrei]
• pkg/statistics/OWNERS [hawkingrei]

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[purelind]

/test build

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[winoros]

/retest