Added Spawn plugin

[ahcorde]

🎉 New feature

Summary

It allows to create entities (models and lights) inside the minimalScene.

Require this PR gazebosim/gz-gui#273

Test it

ign gazebo -r -v 4 minimal_scene.sdf

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• 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

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[codecov]

Codecov Report

Merging #983 (f82ec2e) into main (f48085b) will decrease coverage by 0.01%.
The diff coverage is n/a.

❗ Current head f82ec2e differs from pull request most recent head d93a125. Consider uploading reports for the commit d93a125 to get more accurate results

@@            Coverage Diff             @@
##             main     #983      +/-   ##
==========================================
- Coverage   63.80%   63.78%   -0.02%     
==========================================
  Files         246      246              
  Lines       20015    19996      -19     
==========================================
- Hits        12771    12755      -16     
+ Misses       7244     7241       -3     

Impacted Files	Coverage Δ
src/EntityComponentManager.cc	84.64% <0.00%> (-0.20%)	⬇️
src/SimulationRunner.cc	93.90% <0.00%> (-0.03%)	⬇️
...e/ignition/gazebo/detail/EntityComponentManager.hh	95.10% <0.00%> (+1.68%)	⬆️

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[chapulina]

Works for me! I just ran into a couple of issues:

1. When I click to insert, it looks like I selected an entity with an invalid ID:

   

2. While inserting multiple things, sometimes the hover would stop working, but I'm having a hard time reproducing

3. I got this exception on close:

   [GUI] [Dbg] [MinimalScene.cc:343] Destroy scene [scene]
   terminate called after throwing an instance of 'Ogre::InternalErrorException'
     what():  OGRE EXCEPTION(7:InternalErrorException): MovableObject ID: 194, named 'double_pendulum_with_base_0::lower_link::vis_cylinder_scene::Cylinder(60560)' of type 'Item'
   Had it's mGlobalIndex out of date!!! (or the MovableObject wasn't created with this SceneManager) in SceneManager::checkMovableObjectIntegrity at /var/lib/jenkins/workspace/ogre-2.1-debbuilder/repo/OgreMain/src/OgreSceneManager.cpp (line 4365)
   

[ahcorde]

@chapulina I have a patch but I would like to merge this PR first #995 which is a fix in select entities plugin

[chapulina]

There are some new test failures that seem to be related to SDFormat, unrelated to this PR.