refactor route step / intermediate intersections

rename intersection (engine version) to IntermediateIntersection
follow coding convention for existing functions, move invalidate into routeStep
moved elongate into route step
move forward-step-signage into route step
replace post-processings `forwardInto` with `RouteStep` functionality. Don't change maneuver in step
separete declaration and implementation

src/util/guidance/turn_bearing.cpp

@@ -14,7 +14,8 @@ constexpr double bearing_scale = 360.0 / 256.0;
 // discretizes a bearing into distinct units of 1.4 degrees
 TurnBearing::TurnBearing(const double value) : bearing(value / bearing_scale)
 {
-    BOOST_ASSERT_MSG(value >= 0 && value < 360.0, "Bearing value needs to be between 0 and 360 (exclusive)");
+    BOOST_ASSERT_MSG(value >= 0 && value < 360.0,
+                     "Bearing value needs to be between 0 and 360 (exclusive)");
 }
 
 double TurnBearing::Get() const { return bearing * bearing_scale; }