Fix inconsistent mapping of NeTEx quay publicCode

[hannesj]

Summary

Currently the NeTEx publicCode is mapped to the stop's code. The value is the platform number, and should be mapped to platformCode instead.

Issue

Closes #3141

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.94%. Comparing base (a00b5b3) to head (8a3b289).
⚠️ Report is 16404 commits behind head on dev-2.x.

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #4282      +/-   ##
=============================================
- Coverage      56.95%   56.94%   -0.01%     
- Complexity     10631    10636       +5     
=============================================
  Files           1414     1415       +1     
  Lines          57373    57421      +48     
  Branches        6623     6624       +1     
=============================================
+ Hits           32674    32697      +23     
- Misses         22701    22730      +29     
+ Partials        1998     1994       -4     

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