expression: use cloned RetType at evaluateExprWithNull when it may be changed. (#35759)

[ti-srebot]

cherry-pick #35759 to release-5.3
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/35779

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git push git@github.com:ti-srebot/tidb.git pr/35779:release-5.3-1f40fc72a586

---

What problem does this PR solve?

Issue Number: close #25813

Problem Summary:

evaluateExprWithNull will pass the expression's RetType to NewFunctionInternal, which may change it unexpectedly.

What is changed and how it works?

pass its clone instead of itself.

Check List

Tests

• Unit test
• Integration test

Release note

Fixed a bug that may cause comparisons between json and string report.

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[ti-chi-bot]

@ti-srebot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-srebot]

/run-all-tests

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