With the `ghc::filesystem` dependency from the previous commit. If we
can replace the rest of the Boost.Filesystem dependency then we can get
rid the one nasty runtime dependency we have, and it will make
implementing the chainloading simpler since can reuse more code without
bringing in Boost.
I'm not a fan of Hungarian notation, but C++ kind of needs it with its
implicit `this`. And of all the common options for this, I find
suffixing members with an underscore the least offensive one.
I blindly assumed the original implementation also did this, but this
version `std::variant<Ts...>` objects from being reinitialized if we're
deserializing a variant that's also currently active in the object we're
deserializing into. For simple structs this won't make any difference,
but in yabridge we often use variants to differentiate between things
like single precision and double precision audio buffers. Those buffers
are allocated on the heap, so recreating the objects every time we
deserialize them adds a lot of unnecessary overhead.