Fix msg printer for arrays

[v4hn]

I put this patch here for visibility. @rhaschke pushed it to the ROS-O fork last year.

Robert: Maybe you can comment with an example for completeness? I believe this is related to message parsing in the context of MTC properties, right?

[v4hn]

Related to https://github.com/ros-o/roscpp_core/commits/obese-devel/ (https://github.com/ros-o/roscpp_core/commit/bdb975df0ef48c66c0327cf7d10fda8b1857491f, https://github.com/ros-o/roscpp_core/commit/fe4988788f0bf12b8128bcb6f0eb0fe3707bb6ed, https://github.com/ros-o/roscpp_core/commit/cae00b47f0d6cdbd7712fd4b4e223d49f784c8f0)

[rhaschke]

Printing messages via the ostream operator << doesn't yield valid yaml in roscpp (while it does in rospy). For example, given these simple messages:

main.msg:

uint32[] ints
sub[] subs

sub.msg:

uint32  i
float32 f

yields the following output for std::cout << msg in ROS Noetic:

  ints[]
    ints[0]: 1
    ints[1]: 2
    ints[2]: 3
  subs[]
    subs[0]: 
      i: 0
      f: 0
    subs[1]: 
      i: 0
      f: 0

while it should look like this (to be compatible with rospy/yaml and realized by this PR in ROS One):

  ints: [1, 2, 3]
  subs: 
    -
      i: 0
      f: 0
    -
      i: 0
      f: 0

I remember having seen even worse formatting, but I can't reproduce that quickly.

[rhaschke]

@sloretz: Why did you force-pushed noetic-devel back to kinetic-devel and then re-released as 0.7.1 ??? This is actually the reason for the conflicts in CHANGELOG.rst and package.xml, which I didn't touch originally.

To maintain the release history (including 0.7.0 released by Geoffrey in Sep 2022), I suggest that you revert your force-push. Alternatively, I will rebase my commit onto 0.7.1. Please tell me, how to proceed.

[sloretz]

I will rebase my commit onto 0.7.1. Please tell me, how to proceed.

Oops. Please rebase onto 0.7.1.

I remember doing something unusual with a couple repositories, but I forget why. I vaguely remember thinking tags had been created on the wrong commit and never bloom-released, but gencpp 0.7.0 was released into Noetic https://github.com/ros/rosdistro/pull/34663 . I agree I shouldn't have done that here.

[rhaschke]

@sloretz: I rebased, but using a new branch (I don't want to disrupt the ROS-O release). Please close this PR here and use #58 instead.

[sloretz]

Closing in favor of #58