projection: Return correct collation information

[dbussink]

When we have a project, we correctly convert the value to the connection collation using:

c.Value(vcursor.ConnCollation())

But we then don't update / change the collation on the fields information. This needs to match the actual data, otherwise the client might corrupt the data.

This ensures we add the same rules for the resulting collation.

Related Issue(s)

Fixes #15800

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• Tests were added or are not required
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• Documentation was added or is not required

[vitess-bot]

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[dbussink]

Marked this for back porting, since this can lead to the clients corrupting data / interpreting it as wrongly encoded information and could unexpectedly error out.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.42%. Comparing base (8f6cfaa) to head (d5960cf).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15801      +/-   ##
==========================================
- Coverage   68.42%   68.42%   -0.01%     
==========================================
  Files        1558     1558              
  Lines      196036   196039       +3     
==========================================
+ Hits       134136   134137       +1     
- Misses      61900    61902       +2     

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