Add dependency on ament_index_cpp to resolve build error in ROS 2

[TakashiSato]

This PR adds a dependency on ament_index_cpp to the package to resolve a build error encountered in ROS 2.
The missing dependency was causing issues during the build process, specifically related to including headers from ament_index_cpp.
Adding this dependency ensures that the necessary components are available for successful compilation.

Testing Environment

OS: Ubuntu 24.04 (Docker)
ROS 2: Jazzy

Build Error Log

The following is the build error log that prompted this change:

Starting >>> choreonoid_ros
--- stderr: choreonoid_ros
/home/ubuntu/ws_cnoid/src/choreonoid_ros/src/node/choreonoid_ros2.cpp:1:10: fatal error: ament_index_cpp/get_package_prefix.hpp: No such file or directory
    1 | #include <ament_index_cpp/get_package_prefix.hpp>
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
gmake[2]: *** [src/node/CMakeFiles/choreonoid.dir/build.make:76: src/node/CMakeFiles/choreonoid.dir/choreonoid_ros2.cpp.o] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:185: src/node/CMakeFiles/choreonoid.dir/all] Error 2
gmake[1]: *** Waiting for unfinished jobs....
/home/ubuntu/ws_cnoid/src/choreonoid_ros/src/plugin/BodyROS2Item.cpp: In member function ‘void cnoid::BodyROS2Item::update3DRangeSensor(cnoid::RangeSensor*, rclcpp::Publisher<sensor_msgs::msg::PointCloud2_<std::allocator<void> > >::SharedPtr)’:
/home/ubuntu/ws_cnoid/src/choreonoid_ros/src/plugin/BodyROS2Item.cpp:681:22: warning: unused variable ‘sinPitchAngle’ [-Wunused-variable]
  681 |         const double sinPitchAngle = sin(pitchAngle);
      |                      ^~~~~~~~~~~~~
gmake: *** [Makefile:146: all] Error 2

Changes

Updated package.xml and CMakeLists.txt to include ament_index_cpp as a dependency.

Testing

Successfully built and tested the package with the new dependency included.
Verified that the build error is no longer present after the addition of the dependency.

[s-nakaoka]

Sorry, I had committed the fix for this issue in commit 8d2b078 without noticing your pull request. However, the change to package.xml wasn't included, so I've incorporated your correction for that part ( de948af ). Thanks for your cooperation.

[TakashiSato]

No problem at all, I’m glad to hear that the issue has been resolved. I will go ahead and close this PR.