Latched Strings for URDF and SRDF

[DLu]

Description

Initial solution for #755 / #169

• Adds the rdf_loader::StringLoader class which loads a string from the ROS environment, either via parameter or topic (could theoretically be extended for dynamic parameter later)
• Uses the above functionality to load robot_description and robot_description_semantic
• Adds a parameter to optionally publish a std_msgs::msg::String if read in from a parameter.
• You can also add callback hooks so that the class that uses RDFLoader can take appropriate actions when the description is updated.

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference

[DLu]

I tested with this branch of moveit_resources and the command ros2 launch moveit_resources_panda_moveit_config demo.launch.py

[codecov]

Codecov Report

Merging #765 (c7c2cd5) into main (a4066b0) will increase coverage by 0.06%.
The diff coverage is 74.47%.

@@            Coverage Diff             @@
##             main     #765      +/-   ##
==========================================
+ Coverage   60.79%   60.85%   +0.06%     
==========================================
  Files         271      273       +2     
  Lines       23823    23880      +57     
==========================================
+ Hits        14482    14529      +47     
- Misses       9341     9351      +10     

Impacted Files	Coverage Δ
moveit_ros/planning/rdf_loader/src/rdf_loader.cpp	25.78% <57.15%> (+2.31%)	⬆️
...g/rdf_loader/src/synchronized_string_parameter.cpp	84.22% <84.22%> (ø)
.../rdf_loader/include/moveit/rdf_loader/rdf_loader.h	100.00% <100.00%> (ø)
.../moveit/rdf_loader/synchronized_string_parameter.h	100.00% <100.00%> (ø)
...nning_scene_monitor/src/planning_scene_monitor.cpp	46.11% <0.00%> (-0.47%)	⬇️

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[henningkayser]

Implementation looks good to me so far. We should get a version of this feature merged to unblock MSA work, I would only like to at least make sure the API is compatible with switching to using synced parameters in the future. With this implementation, I don't see too many issues with this, though.

SRDF and URDF need to be checked for compatibility, otherwise the callbacks are risky to use. Possibly switch to using a single callback that triggers when both values are present.

Do the topics use a global namespace?

[DLu]

One thing I'm pondering is how to specify parameters while maintaining maximum compatibility. The goal was to keep the Node based constructor the same, so lines like this didn't have to change:

rdf_loader_.reset(new rdf_loader::RDFLoader(node_, robot_description_property_->getStdString()));

But if we want to have robot_state_display update when a new robot description is published, we need to set the _continuous parameter.... or add something to the constructor to allow bypassing/overriding the parameter check.

[mergify]

This pull request is in conflict. Could you fix it @DLu?

[tylerjw]

I generally really like this. I just have a small question about the base QoS you are using.

[DLu]

Added documentation in moveit/moveit2_tutorials#234