Fix #22703, see #22695, #22704: 90° offset of icon-rotation: way; in mapcss (patch by Woazboat, modified)
This is due to Geometry.getSegmentAngle getting the rotation from the positive
x-axis instead of the positive y-axis, but this is easily corrected by
subtracting 90 degrees (pi/2) from the calculation.
The previous behavior differed from the static rotation angle behavior, which
uses the positive y-axis.