Fix week number for date_format evalengine function

[GuptaManan100]

Description

This PR fixes the way evalengine finds the week for the date_format function. It was noticed that the Week() function works fine, but we weren't using it. This PR changes that to fix the issue ran into in #17431.

Related Issue(s)

• Fixes Bug Report: Incorrect result for Date_format for a week of the year #17431

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

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[vitess-bot]

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[GuptaManan100]

I can make the same change for the other fmtWeek functions. Haven't done that yet, but i think it makes sense to just use the same implementation for everything.

[dbussink]

@GuptaManan100 i think we should do that indeed. Makes it less error prone and the week function afaik is already better tested too.

[dbussink]

@GuptaManan100 Pushed up the fix to always used the documented mode number.

[GuptaManan100]

I'm not sure about the backports either. Do we need to backport this fix to older releases?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.66%. Comparing base (059d01a) to head (e9f9d0b).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17432      +/-   ##
==========================================
- Coverage   67.68%   67.66%   -0.02%     
==========================================
  Files        1583     1583              
  Lines      254321   254363      +42     
==========================================
- Hits       172131   172122       -9     
- Misses      82190    82241      +51     

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[dbussink]

I'm not sure about the backports either. Do we need to backport this fix to older releases?

Don't have a super strong opinion, we could back port to v21 only as a small bugfix?