*: add infoschema.referential_constraints

[morgo]

What problem does this PR solve?

Issue Number: close #26111

Problem Summary:

Ruby on rails depends on infoschema.referential_constraints existing, but it's currently empty in TiDB.

This implements it as much as currently possible. There are some limitations because the constraint schema is not currently populated in fk info, and the constraint name is always specified as "PRIMARY".

What is changed and how it works?

What's Changed:

Support for information_schema.referential_constraints has been added. Previously this table existed but always returned empty results.

Check List

Tests

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

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
  Need to document this table is now supported.
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

• Support for information_schema.referential_constraints has been added. Previously this table existed but always returned empty results.

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• bb7133
• xhebox

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[morgo]

/run-check_dev_2

[bb7133]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 7bd6c12

[ti-chi-bot]

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