file-sys: Default heavy-weight class destructors in the cpp file

Several classes have a lot of non-trivial members within them, or don't
but likely should have the destructor defaulted in the cpp file for
future-proofing/being more friendly to forward declarations.

Leaving the destructor unspecified allows the compiler to inline the
destruction code all over the place, which is generally undesirable from
a code bloat perspective.

src/core/file_sys/vfs_offset.cpp

@@ -14,6 +14,8 @@ OffsetVfsFile::OffsetVfsFile(std::shared_ptr<VfsFile> file_, std::size_t size_,
     : file(file_), offset(offset_), size(size_), name(std::move(name_)),
       parent(parent_ == nullptr ? file->GetContainingDirectory() : std::move(parent_)) {}
 
+OffsetVfsFile::~OffsetVfsFile() = default;
+
 std::string OffsetVfsFile::GetName() const {
     return name.empty() ? file->GetName() : name;
 }