Make dartsim/World.hh header private

[j-rivero]

Move dartsim/World.hh header out from public headers to be in src/ as a private header as suggested long ago in #274 (comment)

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #551 (8961281) into gz-physics7 (9165154) will not change coverage.
Report is 1 commits behind head on gz-physics7.
The diff coverage is n/a.

❗ Current head 8961281 differs from pull request most recent head ab38813. Consider uploading reports for the commit ab38813 to get more accurate results

@@             Coverage Diff              @@
##           gz-physics7     #551   +/-   ##
============================================
  Coverage        76.89%   76.89%           
============================================
  Files              140      140           
  Lines             7683     7683           
============================================
  Hits              5908     5908           
  Misses            1775     1775           

Files	Coverage Δ
dartsim/src/World.hh	100.00% <ø> (ø)

[azeey]

After this PR, would the libgz-physics7-dartsim-dev package become obsolete?

[scpeters]

After this PR, would the libgz-physics7-dartsim-dev package become obsolete?

that still holds the cmake config files, so I think it's needed?

• https://github.com/gazebo-release/gz-physics7-release/blob/main/ubuntu/debian/libgz-physics-dartsim-dev.install

[j-rivero]

After this PR, would the libgz-physics7-dartsim-dev package become obsolete?

that still holds the cmake config files, so I think it's needed?

* https://github.com/gazebo-release/gz-physics7-release/blob/main/ubuntu/debian/libgz-physics-dartsim-dev.install 

that still holds the cmake config files, so I think it's needed?

This is a good point. I think that the main question is: is there a valid use for developers that would generate code from the dartsim plugin that has no public headers? Because we are generating the buildsystem helpers (CMake + pkgconfig) to facilitate that use case. If there is no use case, we either not packaging the helpers and remove the -dev package or change our buildsystem not to generate the helpers.

[j-rivero]

Let's move the conversation to #541