Simplify ament_python_install_package() macro.

[hidmic]

Alternative to #316, #323, #324, #325. This patch no longer delegates to setuptools, it simply builds and installs an .egg-info directory manually. It's a bit hacky, but it's less fragile than the original approach.

CI up to test_communication (to exercise rclpy and rosidl packages):

• Linux
• Linux-aarch64
• macOS
• Windows

CI up to test_communication with --symlink-install:

• Linux
• Linux-aarch64
• macOS
• Windows

[ivanpauno]

Sounds reasonable to me

[hidmic]

Alright, CI is green, reviewer's happy. Going in !

[ivanpauno]

@hidmic I think we should've deleted the test folder, right?

[hidmic]

Yeap. I'll send a PR.

[lukicdarkoo]

@hidmic It seems this PR breaks ability to create Python subpackages. Before (in Foxy) I was able to:

ament_python_install_package(${PROJECT_NAME}/subpackage
  PACKAGE_DIR src/mypackage)

and it would create a subpackage. In Rolling it shows the following error:

09:18:20 CMake Error at /opt/ros/rolling/share/ament_cmake_python/cmake/ament_python_install_package.cmake:98 (add_custom_target):
09:18:20   add_custom_target called with invalid target name
09:18:20   "ament_cmake_python_symlink_webots_ros2_driver/webots".  Target names may
09:18:20   not contain a slash.  Use ADD_CUSTOM_COMMAND to generate files.
09:18:20 Call Stack (most recent call first):
09:18:20   /opt/ros/rolling/share/ament_cmake_python/cmake/ament_python_install_package.cmake:33 (_ament_cmake_python_install_package)
09:18:20   CMakeLists.txt:70 (ament_python_install_package)
09:18:20 
09:18:20 
09:18:20 -- Configuring incomplete, errors occurred!

Is there a workaround or it is broken on purpose?

[ivanpauno]

@hidmic It seems this PR breaks ability to create Python subpackages. Before (in Foxy) I was able to:

IIRC the first argument was always expected to be a package name, which shouldn't contain any / character.
The fact that it accepted / characters at some point was accidental (I think we found a similar issue in a package in the core, but I cannot find the PR).

If you have many package you can still use ament_python_install_package() many times, no need to use / in the package name.
If you have one package with many subpackages you should be using ament_python_install_package() once.