parser: modify parser to support partial index (#63448)

[YangKeao]

This is a cherry-pick of #63448

-> #65698
#65699
#65700

What problem does this PR solve?

Issue Number: close #63447

-> #63448
#62759
#62762

Problem Summary:

What changed and how does it work?

Modify the parser to support partial index grammar

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

❌ Patch coverage is 40.00000% with 6 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-8.5-20260116-v8.5.5@1fa258b). Learn more about missing BASE report.

Additional details and impacted files

@@                       Coverage Diff                        @@
##             release-8.5-20260116-v8.5.5     #65698   +/-   ##
================================================================
  Coverage                               ?   72.4625%           
================================================================
  Files                                  ?       1681           
  Lines                                  ?     469249           
  Branches                               ?          0           
================================================================
  Hits                                   ?     340030           
  Misses                                 ?     106601           
  Partials                               ?      22618           

Flag	Coverage Δ
integration	49.6394% <0.0000%> (?)
unit	64.8664% <40.0000%> (?)

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	55.5569% <0.0000%> (?)

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: winoros
Once this PR has been reviewed and has the lgtm label, please assign bb7133, benmeadowcroft for approval. For more information see the Code Review Process.
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-01-22 14:55:11.781754013 +0000 UTC m=+678539.395710859: ☑️ agreed by winoros.

[YangKeao]

Let's merge #65700 directly 😮‍💨 .