refactor(crosswalk): clean up the structure and create a brief flowchart

Signed-off-by: Takayuki Murooka <takayuki5168@gmail.com>

Author: takayuki5168

planning/behavior_velocity_planner/autoware_behavior_velocity_crosswalk_module/README.md

@@ -8,6 +8,35 @@ This module judges whether the ego should stop in front of the crosswalk in orde
   ![crosswalk_module](docs/crosswalk_module.svg){width=1100}
 </figure>
 
+## Flowchart
+
+```plantuml
+@startuml
+skinparam monochrome true
+
+title modifyPathVelocity
+start
+:getPathEndPointsOnCrosswalk;
+:applySlowDownByLanleet2Map;
+:applySlowDownByOcclusion;
+:getStaticStopPose;
+:resamplePath;
+:checkStopForCrosswalkUsers;
+:checkStopForStuckVehicles;
+:getNearestStopFactor;
+:setSafe;
+:setDistanceToStop;
+
+if (isActivated() is True?) then (yes)
+  :planGo;
+else (yes)
+  :planStop;
+endif
+
+stop
+@enduml
+```
+
 ## Features
 
 ### Yield the Way to the Pedestrians

planning/behavior_velocity_planner/autoware_behavior_velocity_crosswalk_module/include/autoware/behavior_velocity_crosswalk_module/util.hpp

@@ -97,13 +97,14 @@ std::set<int64_t> getCrosswalkIdSetOnPath(
 
 bool checkRegulatoryElementExistence(const lanelet::LaneletMapPtr & lanelet_map_ptr);
 
-std::vector<geometry_msgs::msg::Point> getPolygonIntersects(
+std::optional<std::pair<geometry_msgs::msg::Point, geometry_msgs::msg::Point>>
+getPathEndPointsOnCrosswalk(
   const PathWithLaneId & ego_path, const lanelet::BasicPolygon2d & polygon,
-  const geometry_msgs::msg::Point & ego_pos, const size_t max_num);
+  const geometry_msgs::msg::Point & ego_pos);
 
 std::vector<geometry_msgs::msg::Point> getLinestringIntersects(
   const PathWithLaneId & ego_path, const lanelet::BasicLineString2d & linestring,
-  const geometry_msgs::msg::Point & ego_pos, const size_t max_num);
+  const geometry_msgs::msg::Point & ego_pos);
 
 std::optional<lanelet::ConstLineString3d> getStopLineFromMap(
   const lanelet::Id lane_id, const lanelet::LaneletMapPtr & lanelet_map_ptr,