install xacro using console_scripts entrypoint

[wmmc88]

This changes xacro to be install using a console_script entrypoint, which now fixes running xacro and ros2 run xacro xacro in windows. linux functionality should be unchanged.

closes #302
supersedes #303

[rhaschke]

Thanks. This looks more promising!
I was thinking about symlinking from lib/xacro to bin instead of installing the file a second time.
Symlinks are not supported in Windows.

[rhaschke]

Looks like the new feature was only released into rolling so far. The backport to galactic was merged on Dec 8th, but not yet released.

[wmmc88]

Looks like the new feature was only released into rolling so far. The backport to galactic was merged on Dec 8th, but not yet released.

Ah i didnt notice this because I use rolling. Does this change need to wait until backports to non-eol distros are released then?

[rhaschke]

Does this change need to wait until backports to non-eol distros are released then?

Yes, I cannot release in this state. I also suggested some changes: ament/ament_cmake#328 (comment)

[Tobias-Fischer]

I think the backport has been released. Could this PR be merged now?

[rhaschke]

I think this is also blocked by ament/ament_cmake#372. Will double check...

[rhaschke]

Closing and reopening to trigger CI.