Upgrade to use upstream Python3 CMake Logic

[tfoote]

This module uses PythonInterp and PythonLibs both were deprecated as of Cmake 3.12

The destination we should use is Python3

Alternatively the new upstream modules may have enough capabilities to not even need this module itself.

[sloretz]

Additional motivation ros2/rosidl_python#137

[sloretz]

Assigned self since I have a little time to look at this.

[sloretz]

@cottsay I notice RHEL8 is using CMake 3.11.4. Is it ok to make packages in ROS Rolling require CMake 3.12? Will ROS Humble target a newer version of RHEL with a newer CMake version?

[cottsay]

It's actually 3.18: ros-infrastructure/rep#323

[clalancette]

@sloretz Did all of the work here get done? Can we close this?

[sloretz]

@sloretz Did all of the work here get done? Can we close this?

No. A lot of the work got done, but this critical piece did not: #7

It's been too long for me to remember what's blocking it.

[Ryanf55]

Hey there, FYI, CMake 3.27 is about to be released, which removes these deprecated modules. On distros with rolling releases like MacOS, this could become a problem shortly.
https://cmake.org/cmake/help/latest/release/3.27.html#deprecated-and-removed-features

[clalancette]

I just merged in #7 , which fixes this problem. So closing.