docs: document unstable icu sort order

[ST-DDT]

Closes #2905

• Check whether the locale data should use locale aware sorting #2905

This PR documents why we cannot sort the locale entries locale aware.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.94%. Comparing base (b4e7d21) to head (6d34cff).

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #2948      +/-   ##
==========================================
- Coverage   99.96%   99.94%   -0.02%     
==========================================
  Files        2987     2987              
  Lines      216052   216052              
  Branches      955      598     -357     
==========================================
- Hits       215975   215942      -33     
- Misses         77      110      +33     

see 2 files with indirect coverage changes