Update SA1200UsingDirectivesMustBePlacedCorrectly to not trigger in files with only global using directives

[bjornhellander]

Fixes #3875

[codecov]

Codecov Report

❌ Patch coverage is 91.89189% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.44%. Comparing base (f5843ae) to head (c688544).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3938      +/-   ##
==========================================
- Coverage   97.44%   97.44%   -0.01%     
==========================================
  Files         926      932       +6     
  Lines      110283   110360      +77     
  Branches     3319     3320       +1     
==========================================
+ Hits       107467   107541      +74     
- Misses       1847     1850       +3     
  Partials      969      969              

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