Use FindPython3 in typesupport packages

[sloretz]

Alternative to ros2/rosidl#615

I think with both ament/ament_cmake#355 and ros2/rosidl#612 being merged yesterday, two sources of packages internally calling find_package(PythonInterp) got removed, but their CI's were run at different times. This replaces the implicit PythonInterp dependency with an explicit finding of Python3.

[sloretz]

Short Windows CI to get a quick answer (build: --packages-up-to builtin_interfaces test: --packages-select rosidl_typesupport_c rosidl_typesupport_cpp builtin_interfaces)

Full CI for a complete answer

• Linux
• Linux-aarch64
• macOS
• Windows

[sloretz]

Short windows CI again, this time including ros2/rosidl_typesupport_fastrtps#78:

Full CI again, this time including ros2/rosidl_typesupport_fastrtps#78

• Linux
• Linux-aarch64
• macOS
• Windows

[ivanpauno]

LGTM with green CI

[emersonknapp]

I'm surprised the nightly linux didn't break - I can't get builds to succeed for message packages

[clalancette]

I'm surprised the nightly linux didn't break - I can't get builds to succeed for message packages

Yes, for reasons I don't understand, it seems to be different for different people. It's working fine for me locally, for instance, and it also worked on Linux and macOS on https://ci.ros2.org/view/nightly/. Regardless, the full CI we are running now should show whether it works on all platforms.

[sloretz]

Windows CI has two test failures not in the previous CI job https://ci.ros2.org/view/nightly/job/nightly_win_rel/2022/#showFailuresLink

projectroot.test_buffer_client_tester.launch.py
test_tf2.TestBufferClient.test_termination

But that's a lot better than failing to build, so I'll merge these PRs.