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

unit_tests/library/limits.cpp

@@ -17,7 +17,10 @@
 
 namespace
 {
-osrm::util::Coordinate getZeroCoordinate() { return {osrm::util::FloatLongitude{0}, osrm::util::FloatLatitude{0}}; }
+osrm::util::Coordinate getZeroCoordinate()
+{
+    return {osrm::util::FloatLongitude{0}, osrm::util::FloatLatitude{0}};
+}
 }
 
 BOOST_AUTO_TEST_SUITE(limits)