[lucafedeli88]

This PR performs the switch from C++17 to C++20. In particular:

Main changes :

• cxx_std_17 has been updated to cxx_std_20 in CMake files (and documentation has been updated accordingly)
• Ubuntu 24.04 instead of 22.04 is now used in CI
• in CI, clang v18 is now used, instead of clang v15
• some new clang-tidy CI tests have been excluded (some of them will be added back in separate PRs)

Minor changes :

• in clang-tidy CI test, superfluous compilation options -fsanitize=address -fsanitize=undefined have been removed (the compiled code is not executed)
• the version of some github action scripts has been updated
• For special functions, the Boost version is marked as default (in a separate PR I will switch to the STL version, but this will probably require updating some tests, since the implementation is slightly different)
• following clang-tidy suggestions std::endl has been replaced with \n
• following clang-tidy suggestions a base type has been selected for two enums
• following clang-tidy suggestions, std::is_same<T,float>::value has been changed to std::is_same_v<T,float>
• some variables have been renamed in python_bindings/pxr_qed.cpp to silence a compiler warning on MacOs

[ax3l]

Thank you, @lucafedeli88 ! Feel free to also create a fresh tag/release at the beginning of May :)