Refactor async server joining with eJoinState enum and dedicated progress UI

Replace the boolean-flag-based async join system with a clean state machine
(eJoinState enum) and move connection progress handling from UIScene_JoinMenu
into UIScene_ConnectingProgress as a dedicated UI class.

Combines the best of two approaches: non-blocking sockets with select()
timeout and SO_RCVTIMEO clearing (prevents random disconnects) with the
upstream's state enum, FinalizeJoin separation, and ConnectingProgress UI.

JoinGame() now returns JOINGAME_PENDING on Win64, and
PlatformNetworkManagerStub::DoWork() polls the join state to finalize
the connection when the background thread succeeds.

Minecraft.Client/Common/Network/GameNetworkManager.h

@@ -47,7 +47,8 @@ public:
 	{
 		JOINGAME_SUCCESS,
 		JOINGAME_FAIL_GENERAL,
-		JOINGAME_FAIL_SERVER_FULL
+		JOINGAME_FAIL_SERVER_FULL,
+		JOINGAME_PENDING
 	} eJoinGameResult;
 
 	void			Initialise();
@@ -106,10 +107,6 @@ public:
 	bool			JoinGameFromInviteInfo( int userIndex, int userMask, const INVITE_INFO *pInviteInfo);
 	eJoinGameResult	JoinGame(FriendSessionInfo *searchResult, int localUsersMask);
 	static void		CancelJoinGame(LPVOID lpParam); // Not part of the shared interface
-#ifdef _WINDOWS64
-	bool			BeginJoinGameAsync(FriendSessionInfo *searchResult, int localUsersMask);
-	int				FinishJoinGame(FriendSessionInfo *searchResult);
-#endif
 	bool			LeaveGame(bool bMigrateHost);
 	static int		JoinFromInvite_SignInReturned(void *pParam,bool bContinue, int iPad);
 	void			UpdateAndSetGameSessionData(INetworkPlayer *pNetworkPlayerLeaving = nullptr);