mdl: always enable and make it read only in nextgen

[D3Hunter]

What problem does this PR solve?

Issue Number: ref #61702

Problem Summary:

What changed and how does it work?

as title

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

[tiprow]

Hi @D3Hunter. Thanks for your PR.

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[codecov]

Codecov Report

❌ Patch coverage is 60.52632% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.7295%. Comparing base (5f051c7) to head (f813db3).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #62865        +/-   ##
================================================
+ Coverage   72.7927%   74.7295%   +1.9368%     
================================================
  Files          1792       1838        +46     
  Lines        487597     495809      +8212     
================================================
+ Hits         354935     370516     +15581     
+ Misses       111041     102173      -8868     
- Partials      21621      23120      +1499     

Flag	Coverage Δ
integration	48.7465% <28.9473%> (?)
unit	72.1601% <60.5263%> (-0.0170%)	⬇️

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

Components	Coverage Δ
dumpling	52.8700% <ø> (ø)
parser	∅ <ø> (∅)
br	63.0652% <ø> (+16.7410%)	⬆️

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[Benjamin2037]

LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-08-07 02:27:28.661259164 +0000 UTC m=+494358.804020339: ☑️ agreed by Benjamin2037.
• 2025-08-07 03:27:50.487497861 +0000 UTC m=+497980.630259026: ☑️ agreed by lance6716.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, hawkingrei, lance6716, yudongusa

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Details

Needs approval from an approver in each of these files:

• OWNERS [Benjamin2037,hawkingrei,lance6716]
• pkg/ddl/OWNERS [Benjamin2037]
• pkg/infoschema/OWNERS [Benjamin2037]
• pkg/planner/OWNERS [hawkingrei]
• pkg/sessionctx/vardef/OWNERS [yudongusa]
• pkg/sessionctx/variable/OWNERS [yudongusa]
• pkg/table/OWNERS [Benjamin2037]

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