[Core/Quest] Update quest Objective status Client side

by @untaught; closes #12172

AreaExploredOrEventHappens does not update client side, only server side.
Before adding this fix, it is necessary to complete the required number of kills
to receive the "discovery" Quest Objective Credit in player's Quest Log and on screen.

src/server/game/Entities/Player/Player.cpp

@@ -16373,6 +16373,8 @@ void Player::AreaExploredOrEventHappens(uint32 questId)
             {
                 q_status.Explored = true;
                 m_QuestStatusSave[questId] = QUEST_DEFAULT_SAVE_TYPE;
+                SetQuestSlotState(log_slot, QUEST_STATE_COMPLETE);
+                SendQuestComplete(questId);
             }
         }
         if (CanCompleteQuest(questId))