Check transport mode when mapping GroupStops

[vpaturet]

Summary

As detailed in #5506, when mapping "fixedStopAreaWide" FlexibleStopPlaces (i.e. "UnrestrictedPublicTransportAreas" stop areas), group stops should include only regular stops that match the transport mode of the FlexibleStopPlace.

Note: The Nordic NeTEx profile defines the transport mode as a mandatory field of a FlexibleStopPlace. If the transport mode is unset or unknown in the input dataset, no stop will be mapped.

Issue

Closes #5506

Unit tests

Updated unit tests.

Documentation

No.

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (c706466) 66.93% compared to head (85e8f71) 66.95%.
Report is 87 commits behind head on dev-2.x.

Files	Patch %	Lines
...opentripplanner/netex/mapping/FlexStopsMapper.java	63.63%	2 Missing and 2 partials ⚠️
...pplanner/framework/collection/CollectionUtils.java	71.42%	1 Missing and 1 partial ⚠️
...pentripplanner/api/mapping/SystemNoticeMapper.java	0.00%	1 Missing ⚠️
...n/java/org/opentripplanner/model/SystemNotice.java	50.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #5518      +/-   ##
=============================================
+ Coverage      66.93%   66.95%   +0.01%     
- Complexity     15700    15794      +94     
=============================================
  Files           1819     1832      +13     
  Lines          70248    70540     +292     
  Branches        7392     7410      +18     
=============================================
+ Hits           47022    47229     +207     
- Misses         20772    20840      +68     
- Partials        2454     2471      +17     

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[leonardehrenfried]

This looks good but please add some annotations for clarity and consider my suggestion.