[shared] Use CultureInfo.InvariantCulture in TagWriter

[CodeBlanch]

Relates to #5585 (comment)

Changes

• Use CultureInfo.InvariantCulture when calling Convert.ToString for tag/attribute values without explicit handling.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.06%. Comparing base (6250307) to head (9db1e7e).
Report is 264 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5700      +/-   ##
==========================================
+ Coverage   83.38%   86.06%   +2.68%     
==========================================
  Files         297      254      -43     
  Lines       12531    11054    -1477     
==========================================
- Hits        10449     9514     -935     
+ Misses       2082     1540     -542     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	85.98% <ø> (?)
unittests-Project-Stable	86.05% <ø> (?)
unittests-Solution	86.05% <ø> (?)
unittests-UnstableCoreLibraries-Experimental	84.54% <ø> (?)

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see 124 files with indirect coverage changes