Relax rejection of GTFS flex trips that also contain continuous stopping

[leonardehrenfried]

Summary

This brings OTP in line with the GTFS spec by allowing flex and continuous stopping in the same trip as long as it's not mixed in the very same stop time.

There is also a small improvement to the debug UI where routes without a publicCode/shortName use the long name as the fallback.

Issue

Closes #6230

Unit tests

The majority of the code is test refactoring. Lots of tests for this behavior added.

Documentation

n/a

Bumping the serialization version id

I'm changing static method on a file that is being serialised so I'm bumping just in case.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 69.75%. Comparing base (87b6a46) to head (8f6ba7b).

Files with missing lines	Patch %	Lines
.../org/opentripplanner/ext/flex/FlexTripsMapper.java	50.00%	0 Missing and 1 partial ⚠️
...ipplanner/ext/flex/trip/ScheduledDeviatedTrip.java	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #6231      +/-   ##
=============================================
- Coverage      69.75%   69.75%   -0.01%     
  Complexity     17652    17652              
=============================================
  Files           2007     2007              
  Lines          75563    75561       -2     
  Branches        7731     7730       -1     
=============================================
- Hits           52711    52707       -4     
- Misses         20141    20146       +5     
+ Partials        2711     2708       -3     

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[leonardehrenfried]

@m-mcqueen @fpurcell If you want to you can try out this version and deploy it to your servers before review has concluded.