Refactor command utilities to class methods

[PragmaTwice]

Class outline:

struct CommandTable {
 public:
  CommandTable() = delete;

  static CommandMap *Get();
  static const CommandMap *GetOriginal();
  static void Reset();

  static void GetAllCommandsInfo(std::string *info);
  static void GetCommandsInfo(std::string *info, const std::vector<std::string> &cmd_names);
  static std::string GetCommandInfo(const CommandAttributes *command_attributes);
  static Status GetKeysFromCommand(const CommandAttributes *attributes, const std::vector<std::string> &cmd_tokens,
                                   std::vector<int> *keys_indexes);

  static size_t Size();
  static bool IsExists(const std::string &name);

  static Status ParseSlotRanges(const std::string &slots_str, std::vector<SlotRange> &slots);

 private:
  static inline std::deque<CommandAttributes> redis_command_table;

  // Original Command table before rename-command directive
  static inline CommandMap original_commands;

  // Command table after rename-command directive
  static inline CommandMap commands;

  friend struct RegisterToCommandTable;
};

[torwig]

LGTM.