refactor(Core/World): Create WorldSessionMgr to split session logic out of World (#21400)

src/server/game/Battlegrounds/Arena.cpp

@@ -25,6 +25,7 @@
 #include "ScriptMgr.h"
 #include "World.h"
 #include "WorldSession.h"
+#include "WorldSessionMgr.h"
 //#include "WorldStatePackets.h"
 
 void ArenaScore::AppendToPacket(WorldPacket& data)
@@ -224,7 +225,7 @@ void Arena::EndBattleground(TeamId winnerTeamId)
         {
             // pussywizard: arena logs in database
             uint32 fightId = sArenaTeamMgr->GetNextArenaLogId();
-            uint32 currOnline = sWorld->GetActiveSessionCount();
+            uint32 currOnline = sWorldSessionMgr->GetActiveSessionCount();
 
             CharacterDatabaseTransaction trans = CharacterDatabase.BeginTransaction();
             CharacterDatabasePreparedStatement* stmt2 = CharacterDatabase.GetPreparedStatement(CHAR_INS_ARENA_LOG_FIGHT);