Guard boost::filesystem usage

[simmplecoder]

Description

CMake was unopinionated about what filesystem is used and required excessive flag setting. Now it clarifies that boost::filesystem is default and std::filesystem is used in case BOOST_GIL_USE_BOOST_FILESYSTEM is off and CMAKE_CXX_STANDARD>=17.

Apparently we did not explicitly linked to boost libraries anyway. Either that, or I overlooked it.

References

https://github.com/boostorg/gil/issues/742

Tasklist

• [ ] Add test case(s)
• [ ] Ensure all CI builds pass
• [ ] Review and approve

[mloskot]

I think this is what we need, thank you!