Improve standalone examples (and a bit of example CMake)

[Ryanf55]

Docs

Summary

• Simpler and standard build workflow
• Utilize CTest with the recommended workflow of optional tests
• Skip using make directly so these become more platform portable
• Skip having to manually create the build directory
• Do all operations from the source directory when possible to reduce the number of commands
• Surround commands in bash tags to get syntax highlighting

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.

[azeey]

Can you fix the conflict on examples/standalone/gtest_setup/CMakeLists.txt?

[Blast545]

:farmer: @Ryanf55 I was taking a look to this to fix our CI, it's pretty close to be mergeable, let us know if you need help with the remaining conflicts :rocket:

[Ryanf55]

Looks like gtest can't be found in CI. Should I be making changes to the local CI, or is this managed elsewhere? https://build.osrfoundation.org/job/gz_sim-ci-pr_any-jammy-amd64/610/cmake/new/

[azeey]

Looks like gtest can't be found in CI. Should I be making changes to the local CI, or is this managed elsewhere? https://build.osrfoundation.org/job/gz_sim-ci-pr_any-jammy-amd64/610/cmake/new/

I think it's best to revert your changes. I don't think we're prepared to change our CI for this.