Concatenates all segment point arrays from a route into a single flat array.
Carefully avoids duplicating the shared boundary point between adjacent segments —
if the first point of a new segment equals the last point of the previous one, it is skipped.
Concatenates all segment point arrays from a route into a single flat array. Carefully avoids duplicating the shared boundary point between adjacent segments — if the first point of a new segment equals the last point of the previous one, it is skipped.