expression: correct constant propagation for collation (#22666)

[ti-srebot]

cherry-pick #22666 to release-4.0
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/22923

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---

Signed-off-by: wjhuang2016 huangwenjun1997@gmail.com

What problem does this PR solve?

Issue Number: close #22665

Problem Summary:
Check the collation more strictly.

What is changed and how it works?

Propagate constant only if their collations are strictly equal.

Related changes

• Need to cherry-pick to the release branch

Check List

Tests

• Unit test

Side effects

Release note

• fix a bug may cause wrong constant propagation and get the wrong result.

[ti-srebot]

/run-all-tests

[ti-srebot]

@wjhuang2016 you're already a collaborator in bot's repo.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• qw4990
• winoros

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[zhouqiang-cl]

/merge

[ti-chi-bot]

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

Commit hash: 31b13ee

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