Restore CXX_STANDARD 17 in core library

[scpeters]

🦟 Bug fix

Restore CXX_STANDARD export in core library that was removed in #1059 and also tests gazebosim/gz-cmake#273

Summary

This is mainly testing gazebosim/gz-cmake#273 using the ci_matching_branch/ trickery with osrf/homebrew-simulation@406b74a and gazebo-tooling/gazebodistro@b427433, but it does make a small improvement of its own, restoring the CXX_STANDARD export. The main things changed in gazebosim/gz-cmake#273 is finding IgnURDFDOM changes to GzURDFDOM, but there may be an issue with the target names not being migrated. This is a draft PR until that is confirmed.

Checklist

• Signed all commits for DCO
• Added tests
• 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 #1072 (1fd9d56) into main (fdd9861) will not change coverage.
The diff coverage is n/a.

❗ Current head 1fd9d56 differs from pull request most recent head d74d0f3. Consider uploading reports for the commit d74d0f3 to get more accurate results

@@           Coverage Diff           @@
##             main    #1072   +/-   ##
=======================================
  Coverage   83.12%   83.12%           
=======================================
  Files         154      154           
  Lines       18702    18702           
=======================================
  Hits        15546    15546           
  Misses       3156     3156           

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[scpeters]

the homebrew build using gazebosim/gz-cmake#273 didn't find the external URDFDOM package, so it built against the internal fork of URDFDOM, which apparently has some pragma's that cause compiler warnings.

CMake Deprecation Warning at /usr/local/share/cmake/gz-cmake3/cmake3/IgnUtils.cmake:231 (message):
  Ign prefixed package name [IgnURDFDOM] is deprecated! Automatically using
  the Gz prefix instead: [GzURDFDOM]
Call Stack (most recent call first):
  CMakeLists.txt:54 (gz_find_package)


-- Looking for  - found

-- Using internal URDF

[scpeters]

the homebrew build using gazebosim/gz-cmake#273 didn't find the external URDFDOM package, so it built against the internal fork of URDFDOM, which apparently has some pragma's that cause compiler warnings.

upon rebuilding, it appears to be working now, except for the *_pretty variable commented about in gazebosim/gz-cmake#273 (comment)