Explicit convert from std::filesystem::path to std::string for Windows compatibility

[traversaro]

Description

On Linux and macOS std::filesystem::path is implicitly convertible to std::string, while on Windows it is convertible to std::wstring, see https://en.cppreference.com/w/cpp/filesystem/path and https://stackoverflow.com/questions/57377349/implicit-conversion-between-stdfilesystempath-and-stdstring-should-it-hap . If we want to convert std::filesystem::path to std::string in a Windows-compatible way, it is then necessary to explicitly call the .string() method.

Fix part of #2391 .

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

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 36.36364% with 14 lines in your changes missing coverage. Please review.

Project coverage is 45.65%. Comparing base (415a4a2) to head (ceff78c).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...up_core_plugins/src/configuration_files_widget.cpp	0.00%	4 Missing ⚠️
...eit_setup_core_plugins/src/start_screen_widget.cpp	0.00%	3 Missing ⚠️
.../moveit_setup_assistant/src/collisions_updater.cpp	0.00%	2 Missing ⚠️
...sistant/moveit_setup_framework/src/urdf_config.cpp	71.43%	2 Missing ⚠️
...eit_setup_assistant/src/setup_assistant_widget.cpp	0.00%	1 Missing ⚠️
.../moveit_setup_core_plugins/configuration_files.hpp	0.00%	1 Missing ⚠️
...ant/moveit_setup_core_plugins/src/start_screen.cpp	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3249      +/-   ##
==========================================
- Coverage   45.65%   45.65%   -0.00%     
==========================================
  Files         714      714              
  Lines       62298    62297       -1     
  Branches     7532     7531       -1     
==========================================
- Hits        28437    28433       -4     
- Misses      33695    33697       +2     
- Partials      166      167       +1     

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[JafarAbdi]

LGTM

[sea-bass]

I think the clang-tidy check was failing because of the new generate_parameter_library version putting headers elsewhere. Deleted all the repo's build caches and will see how it goes.