feat(autoware_pcl_extensions): porting from universe to core

sensing/autoware_pcl_extensions/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.14)
+project(autoware_pcl_extensions)
+
+find_package(autoware_cmake REQUIRED)
+autoware_package()
+
+find_package(PCL REQUIRED COMPONENTS common)
+find_package(eigen3_cmake_module REQUIRED)
+find_package(Eigen3 REQUIRED)
+
+include_directories(
+  SYSTEM
+    ${EIGEN3_INCLUDE_DIR}
+    ${PCL_INCLUDE_DIRS}
+)
+link_directories(${PCL_LIBRARY_DIRS})
+add_definitions(${PCL_DEFINITIONS})
+
+ament_auto_add_library(autoware_pcl_extensions SHARED
+  src/voxel_grid_nearest_centroid.cpp
+)
+
+target_link_libraries(autoware_pcl_extensions ${PCL_LIBRARIES})
+
+ament_auto_package()

sensing/autoware_pcl_extensions/README.md

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+# autoware_pcl_extensions
+
+## Overview
+
+The `autoware_pcl_extensions` is a pcl extension library. The voxel grid filter in this package works with a different algorithm than the original one.
+
+## Design
+
+Inner-workings / Algorithms
+
+### Original Algorithm [1]
+
+1. create a 3D voxel grid over the input pointcloud data
+2. calculate centroid in each voxel
+3. all the points are approximated with their centroid
+
+### Extended Algorithm
+
+1. create a 3D voxel grid over the input pointcloud data
+2. calculate centroid in each voxel
+3. **all the points are approximated with the closest point to their centroid**
+
+## Inputs / Outputs
+
+input and output are pointcloud with the datatype `pcl::PointCloud<pcl::PointXYZ>`
+
+## Parameters
+
+`leaf_size`: it represents the scale of each cell in 3 dimension.
+
+It can be set by calling this function, where the scale of the cell in the axis of x, y and z are set respectively
+
+```cpp
+filter.setLeafSize(voxel_size_x_, voxel_size_y_, voxel_size_z_);
+```
+
+## Usage
+
+include the header file
+
+```cpp
+#include <autoware/pcl_extensions/voxel_grid_nearest_centroid.hpp>
+```
+
+init the filter with input pointcloud, set leaf size and get output result
+
+```cpp
+pcl::VoxelGridNearestCentroid<pcl::PointXYZ> filter;
+filter.setInputCloud(pcl_input);
+filter.setLeafSize(voxel_size_x_, voxel_size_y_, voxel_size_z_);
+filter.filter(*pcl_output);
+```
+
+## (Optional) References/External links
+
+[1] <https://pointclouds.org/documentation/tutorials/voxel_grid.html>