planner fix: scoping rules for JOIN ON expression inside a subquery

[harshit-gangal]

Description

This PR updates the scoping rules for expressions involved in join table ON clauses, allowing them to use the scope of the SELECT statement's parent scope.

In MySQL 5.7, this scoping rule is not supported. However, MySQL 8.0 and later versions do support this functionality.

For example, consider the following query:

SELECT 1, (SELECT foo FROM t1 JOIN t2 ON t1.col = t2.col AND t1.id = t3.id) subquery FROM t3;

With the updated scoping rules, the join condition between t1 and t2 can now reference columns from t3, essentially allowing access to all columns available from the outer query.

Related Issue(s)

• Fixes Bug: Table name or alias isn't recognized within JOIN of a nested subquery within SELECT clause #12919

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

Deployment Notes

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[vitess-bot]

I was unable to backport this Pull Request to the following branches: release-14.0, release-15.0, release-16.0.