vfs: Make type hierarchy objects classes instead of structs

struct should be used when the data type is very simple or otherwise has
no invariants associated with it. Given these are used to form a
hierarchy, class should be used instead.

src/core/file_sys/vfs.h

@@ -15,9 +15,9 @@
 
 namespace FileSys {
 
-struct VfsFilesystem;
-struct VfsFile;
-struct VfsDirectory;
+class VfsDirectory;
+class VfsFile;
+class VfsFilesystem;
 
 // Convenience typedefs to use Vfs* interfaces
 using VirtualFilesystem = std::shared_ptr<VfsFilesystem>;
@@ -34,7 +34,8 @@ enum class VfsEntryType {
 // A class representing an abstract filesystem. A default implementation given the root VirtualDir
 // is provided for convenience, but if the Vfs implementation has any additional state or
 // functionality, they will need to override.
-struct VfsFilesystem : NonCopyable {
+class VfsFilesystem : NonCopyable {
+public:
     VfsFilesystem(VirtualDir root);
     virtual ~VfsFilesystem();
 
@@ -81,7 +82,8 @@ protected:
 };
 
 // A class representing a file in an abstract filesystem.
-struct VfsFile : NonCopyable {
+class VfsFile : NonCopyable {
+public:
     virtual ~VfsFile();
 
     // Retrieves the file name.
@@ -179,7 +181,8 @@ struct VfsFile : NonCopyable {
 };
 
 // A class representing a directory in an abstract filesystem.
-struct VfsDirectory : NonCopyable {
+class VfsDirectory : NonCopyable {
+public:
     virtual ~VfsDirectory();
 
     // Retrives the file located at path as if the current directory was root. Returns nullptr if
@@ -295,7 +298,8 @@ protected:
 
 // A convenience partial-implementation of VfsDirectory that stubs out methods that should only work
 // if writable. This is to avoid redundant empty methods everywhere.
-struct ReadOnlyVfsDirectory : public VfsDirectory {
+class ReadOnlyVfsDirectory : public VfsDirectory {
+public:
     bool IsWritable() const override;
     bool IsReadable() const override;
     std::shared_ptr<VfsDirectory> CreateSubdirectory(std::string_view name) override;