[foxy] Latched Strings for URDF and SRDF

[DLu]

Description

#765 for foxy (with a little bit of #1050 and #1132)

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
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[mergify]

Please target the main branch for development, we will backport the changes to foxy for you if approved and if they don't break API.

[codecov]

Codecov Report

Merging #1414 (6c3e7e7) into foxy (949face) will increase coverage by 0.29%.
The diff coverage is 72.73%.

@@            Coverage Diff             @@
##             foxy    #1414      +/-   ##
==========================================
+ Coverage   46.79%   47.08%   +0.29%     
==========================================
  Files         185      187       +2     
  Lines       19693    19749      +56     
==========================================
+ Hits         9214     9297      +83     
+ Misses      10479    10452      -27     

Impacted Files	Coverage Δ
.../rdf_loader/include/moveit/rdf_loader/rdf_loader.h	66.67% <0.00%> (+66.67%)	⬆️
moveit_ros/planning/rdf_loader/src/rdf_loader.cpp	52.69% <55.27%> (+31.04%)	⬆️
...g/rdf_loader/src/synchronized_string_parameter.cpp	84.75% <84.75%> (ø)
.../moveit/rdf_loader/synchronized_string_parameter.h	100.00% <100.00%> (ø)

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[vatanaksoytezer]

I'm happy with the changes except that we are changing API here. I would like to make sure @henningkayser @JafarAbdi @tylerjw or any other maintainers are OK with this as well.

[vatanaksoytezer]

Ping to @tylerjw and @henningkayser