FI: Use std::filesystem

[gpx1000]

#462 is a great implementation that depends upon platform specific code for filesystem classes (i.e. windowsFileSystem, unixFileSystem class etc). I would suggest that we can switch to using std::filesystem to provide a common class that takes away the need for platform dependent code.

[TomAtkinsonArm]

I like the idea of doing this. The main thing id want to keep is a standard way of defining virtual paths in the project. I guess now we are using c++17 we might be able to use https://en.cppreference.com/w/cpp/filesystem/path

I dont know enough information about this to implement it.

How hard would this be with the current #462? And can #462 merge without this change and the C++17 Filesystem be added as a separate PR?

[gpx1000]

I think it's fair to do it as a separate PR. It feels like it's a different task and it depends upon C++17 to get fully merged first so why add an extra hurdle to #462?