Enforce matching substate enums to functions

In the main state machine, the matching of the functions to the states is enforced in def_state_info_table.h, e.g.

DEF_STATE_INFO(GAME_STATE_MAIN_MENU,     game_main_menu_on_init,    game_main_menu_on_update,    game_main_menu_on_exit   )

However, for the substates of the various states the definitions of the states and the functions are separate, e.g.

enum GameShopStates
{
    GAME_SHOP_INTRO,
    GAME_SHOP_ACTIVE,
    GAME_SHOP_SHOW_CARD_DESC,
    GAME_SHOP_HIDE_CARD_DESC,
    GAME_SHOP_EXIT,
    GAME_SHOP_MAX
};

static void game_shop_intro(void);
static void game_shop_process_user_input(void);
static void game_shop_show_card_desc(void);
static void game_shop_hide_card_desc(void);
static void game_shop_outro(void);

static StateInfo shop_state_actions[GAME_SHOP_MAX] = {
    STATE_INFO_UPDATE_FN_ONLY(game_shop_intro),
    STATE_INFO_UPDATE_FN_ONLY(game_shop_process_user_input),
    STATE_INFO_UPDATE_FN_ONLY(game_shop_show_card_desc),
    STATE_INFO_UPDATE_FN_ONLY(game_shop_hide_card_desc),
    STATE_INFO_UPDATE_FN_ONLY(game_shop_outro),
};

so it relies on the definitions being at the same order, which can easily go out of sync. This can be mitigated by using the format

static StateInfo shop_state_actions[GAME_SHOP_MAX] = {
    [GAME_SHOP_INTRO] = STATE_INFO_UPDATE_FN_ONLY(game_shop_intro),
...
};

So the connection between state and function is explicit and enforced in the code.