Add metafilesystem hook to add optimized implementations of compute recursive directory size

Core/FileSystems/DirectoryFileSystem.h

@@ -115,6 +115,9 @@ public:
 	FileSystemFlags Flags() override { return flags; }
 	u64 FreeSpace(const std::string &path) override;
 
+	// TODO: Replace with optimized implementation.
+	bool ComputeRecursiveDirSizeIfFast(const std::string &path, int64_t *size) override { return false; }
+
 private:
 	struct OpenFileEntry {
 		DirectoryFileHandle hFile;
@@ -159,6 +162,8 @@ public:
 	FileSystemFlags Flags() override { return FileSystemFlags::FLASH; }
 	u64 FreeSpace(const std::string &path) override { return 0; }
 
+	bool ComputeRecursiveDirSizeIfFast(const std::string &path, int64_t *size) override { return false; }
+
 private:
 	struct OpenFileEntry {
 		u8 *fileData;