[Experimental] GP Mode for 3/4 Players

[MegaMech]

This PR needs to be tested to confirm that it does not introduce new bugs to the game.

Please advise if any bugs are found.

This feature is not the current focus, any bugs related to this new mode will not be investigated (ex. wide-screen UI issues). As such, if this is merged, it's to allow the feature to exist. The capability to play Kalimari Desert with the full train, 4 human players, and 4 CPU players is considered desirable, even if some defects exist.

Concerns

• 3/4 player mode accesses the kart texture buffer in a strange way:
  • buffer[screenIndex][playerIndex] // Normal usage
  • buffer[screenOne][0-3] // Screen 1
  • buffer[screenOne][4-7] // Screen 2
  • buffer[screenTwo][0-3] // Screen 3
  • buffer[screenTwo][4-7] // Screen 4

The above hack (which saves memory) only allows 4 players per screen. Thus some changes have been made to allow drawing 8 players on 3/4 screens.

• Does 2P GP/Versus and 3p/4p versus modes still work properly?

This PR may also pave the way for allowing more than eight player games. However, many arrays and for loops would need to be increased. At the very least, drawing more than eight players should be easily possible.