Add a flexible mechanism to combine user and default plugins

[azeey]

🎉 New feature

Closes #796

Summary

Implementation based on #796 (comment)

TODO:

• Cleanup
• Tests

Test it

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.

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[azeey]

@iche033 Based on your suggestion, I've simplified the various options available.

• For Server plugins, I've removed all of the options and plugins are simply appended to the list. The user can then used the <gz:system_priority> to configure the order the plugins.
• For GUI plugins, since the order of plugins is important but there is no mechanism similar to <gz:system_priority>, I've implemented the following behavior:
  • If the a plugin from the SDF also exists in the default configuration, the plugin from SDF will replace the one in the default configuration at the position/order of the plugin in the default configuration.
  • Otherwise, it's appended to the end

[iche033]

looks good. Works as expected.

originally I was testing with separate <gz:policies> blocks for include_server_config_plugins and include_gui_default_plugins, and was wondering why one of them didn't have an effect. But then realized that only one <gz:policies> can be present in the sdf file. Nothing needs to be done on this, just noting down for reference.

[iche033]

this test failure looks related:

/Users/jenkins/jenkins-agent/workspace/gz_sim-ci-pr_any-homebrew-amd64/gz-sim/src/Server_TEST.cc:514
Expected equality of these values:
  2u
    Which is: 2
  *server.SystemCount()
    Which is: 5
    ```

[iche033]

this test failure looks related:

/Users/jenkins/jenkins-agent/workspace/gz_sim-ci-pr_any-homebrew-amd64/gz-sim/src/Server_TEST.cc:514
Expected equality of these values:
  2u
    Which is: 2
  *server.SystemCount()
    Which is: 5
    ```

my understanding is that an increase in no. of systems is expected due to behavior change. I increased the expected system count to fix the test, in the same way it was done to fix other Server tests.
a0c23f2

[azeey]

this test failure looks related:

/Users/jenkins/jenkins-agent/workspace/gz_sim-ci-pr_any-homebrew-amd64/gz-sim/src/Server_TEST.cc:514
Expected equality of these values:
  2u
    Which is: 2
  *server.SystemCount()
    Which is: 5
    ```

my understanding is that an increase in no. of systems is expected due to behavior change. I increased the expected system count to fix the test, in the same way it was done to fix other Server tests. a0c23f2

INTEGRATION_multiple_severs failed because we were loading the physics systems, but the test explicitly does not want it as indicated by TestWorldSansPhysics. My guess is that by including physics, it gets loaded twice and we run into #18

[iche033]

gz_sim-ci-pr_any-noble-amd64 picked up many new warnings - looks like they are false positives from the new console log msgs. I'm going to merge this since all tests are passing but we should ticket an issue on this

[iche033]

gz_sim-ci-pr_any-noble-amd64 picked up many new warnings - looks like they are false positives from the new console log msgs. I'm going to merge this since all tests are passing but we should ticket an issue on this

#2555