improve spreadType roadCenter

[namdre]

t looks a bit strange when the geometry is adapted due to extra bike lanes or sidewalks. The roadCenter function should be adapted to only shift based on "normal" road lanes

in addition to ignoring sidewalks, bikelanes etc, the roadCenter function should also ignore right-turn lanes to ensure that the straight continuation are aligned.

Another optional feature would be to ensure straight continuation alignment even if one side has more left turn lanes than the other (by setting custom lane geometry to create a gap between directions where the turn lane is missing, with the maximum length of the gap being configurable)

related #6662, #12282