Implement merging nearby turns together.

When there are multiple turns near each other (< 60m), set the lanes
that are allowed on earlier turns such that staying on that lane will
carry you through the other turns.

For a standard left/right turn at a traffic light at two one-way roads
(dual carriageway), this means that the left and right turns are
correctly highlighted.
This evaluates different value that it stays isLeftTurn will return true, in case it is slight left turn