Add highway=platform to IsBoardingLocation()

[Brickblock1]

Summary

Since #6247 it has been possible to link transit data to the streetgraph for linear ways and not just nodes and areas. The list of tags in IsBoardingLocation() was not appropriate for this with regards to buses which use tag highway=platform for linear ways. This PR therefore adds highway=platform to the function.

Issue

Closes #6433

Unit tests

None

Documentation

Docs were updated and now mention both highway=platform and railway=platform in addition to the previous list of tags.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.13%. Comparing base (d6c64e6) to head (485c4e5).
Report is 4 commits behind head on dev-2.x.

Additional details and impacted files

@@            Coverage Diff             @@
##             dev-2.x    #6505   +/-   ##
==========================================
  Coverage      70.13%   70.13%           
- Complexity     18266    18271    +5     
==========================================
  Files           2077     2077           
  Lines          77617    77618    +1     
  Branches        7819     7820    +1     
==========================================
+ Hits           54435    54441    +6     
+ Misses         20402    20400    -2     
+ Partials        2780     2777    -3     

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[vesameskanen]

Could you add a simple unit test here:

application/src/test/java/org/opentripplanner/graph_builder/module/osm/moduletests/BoardingLocationTest.java