expression: set a collation according to the arguments for ifnull in constant folding

[YangKeao]

What problem does this PR solve?

Issue Number: close #51765

Problem Summary:

The ifnull has different behavior in inferring collation for constant folding and normal execution path.

What changed and how does it work?

Set the collation according to the first argument in the path of constant folding.

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.

Release note

Fix the issue that the collation of `ifnull` expression is different with MySQL when constant folding applies.

[codecov]

Codecov Report

Merging #52119 (a050b21) into master (094f4df) will decrease coverage by 15.9751%.
Report is 2 commits behind head on master.
The diff coverage is 100.0000%.

Additional details and impacted files

@@                Coverage Diff                @@
##             master     #52119         +/-   ##
=================================================
- Coverage   70.6856%   54.7105%   -15.9751%     
=================================================
  Files          1486       1597        +111     
  Lines        439484     609164     +169680     
=================================================
+ Hits         310652     333277      +22625     
- Misses       109326     252663     +143337     
- Partials      19506      23224       +3718     

Flag	Coverage Δ
integration	36.6785% <100.0000%> (?)
unit	70.4423% <100.0000%> (-0.0555%)	⬇️

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

Components	Coverage Δ
dumpling	53.9957% <ø> (ø)
parser	∅ <ø> (∅)
br	51.3952% <ø> (+5.5882%)	⬆️

[zanmato1984]

lgtm

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: zanmato1984, zimulala

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• OWNERS [zanmato1984,zimulala]
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-03-26 17:44:15.829955002 +0000 UTC m=+2003482.852201386: ☑️ agreed by zanmato1984.
• 2024-03-27 01:53:09.846229352 +0000 UTC m=+2032816.868475741: ☑️ agreed by zimulala.

[zimulala]

/check-issue-triage-complete

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #52124.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #52130.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #52131.