planner: add back children's Schema when checking LogicalJoin's used columns in column pruning

[time-and-fate]

What problem does this PR solve?

Issue Number: close #60692

Problem Summary:

As said in the issue, sometimes the FullSchema may contain outdated Columns after the projection elimination.

We should have fixed the FullSchema, but considering the long-standing problems in schema maintenance and column pruning in tidb, we can't make sure we won't introduce any new risk.
This PR is likely to be cherry-picked to the LTS version quickly. So it's better to just restore the previous checking logic, i.e., use the Schema() to do the check.

What changed and how does it work?

Add back what's been removed in #51057 in (*LogicalJoin).ExtractUsedCols().

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

[Copilot]

Pull Request Overview

This PR restores the previous logic in LogicalJoin by bringing back the usage of each child’s Schema (via FullSchema) when checking for used columns, addressing cases where outdated columns may persist after projection elimination.

• Introduces local variables lFullSchema and rFullSchema to capture children’s FullSchema.
• Adjusts conditional checks to consider both the original Schema and FullSchema for column containment.

Files not reviewed (2)

• tests/integrationtest/r/planner/core/issuetest/planner_issue.result: Language not supported
• tests/integrationtest/t/planner/core/issuetest/planner_issue.test: Language not supported

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.0250%. Comparing base (8b75529) to head (249cb7a).
Report is 15 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #60694        +/-   ##
================================================
+ Coverage   73.1255%   74.0250%   +0.8994%     
================================================
  Files          1716       1716                
  Lines        475616     479130      +3514     
================================================
+ Hits         347797     354676      +6879     
+ Misses       106435     103055      -3380     
- Partials      21384      21399        +15     

Flag	Coverage Δ
integration	42.9359% <100.0000%> (?)
unit	72.9041% <100.0000%> (+0.5588%)	⬆️

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

Components	Coverage Δ
dumpling	52.6553% <ø> (ø)
parser	∅ <ø> (∅)
br	47.5997% <ø> (+0.1812%)	⬆️

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AilinKid, winoros

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Needs approval from an approver in each of these files:

• OWNERS [AilinKid,winoros]
• pkg/planner/OWNERS [AilinKid,winoros]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-04-22 04:02:48.507792862 +0000 UTC m=+328312.319583242: ☑️ agreed by winoros.
• 2025-04-23 06:40:44.302886913 +0000 UTC m=+424188.114677494: ☑️ agreed by AilinKid.

[AilinKid]

/retest-required

[time-and-fate]

/retest

[time-and-fate]

/cherry-pick release-8.5

[ti-chi-bot]

@time-and-fate: new pull request created to branch release-8.5: #60738.
But this PR has conflicts, please resolve them!

In response to this:

/cherry-pick release-8.5

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