Core/Quests: Implement CMSG_QUEST_NPC_QUERY and SMSG_QUEST_NPC_QUERY_RESPONSE

Plot twist: We don't know what these packets do (but they are used)

src/server/game/Handlers/QueryHandler.cpp

@@ -419,6 +419,45 @@ void WorldSession::HandleCorpseMapPositionQuery(WorldPacket& recvData)
     SendPacket(&data);
 }
 
+void WorldSession::HandleQuestNPCQuery(WorldPacket& recvData)
+{
+    uint32 count = recvData.ReadBits(24);
+    std::map<uint32, std::vector<uint32>> quests;
+
+    for (int i = 0; i < count; ++i)
+    {
+        uint32 questId;
+        recvData >> questId;
+
+        /// @todo verify if we should only send completed quests questgivers
+        if (_player->GetQuestStatus(questId) == QUEST_STATUS_COMPLETE)
+        {
+            auto creatures = sObjectMgr->GetCreatureQuestInvolvedRelationReverseBounds(questId);
+            for (auto it = creatures.first; it != creatures.second; ++it)
+                quests[questId].push_back(it->second);
+
+            auto gos = sObjectMgr->GetGOQuestInvolvedRelationReverseBounds(questId);
+            for (auto it = gos.first; it != gos.second; ++it)
+                quests[questId].push_back(it->second | 0x80000000); // GO mask
+        }
+    }
+
+    WorldPacket data(SMSG_QUEST_NPC_QUERY_RESPONSE, 3 + count * 14);
+    data.WriteBits(quests.size(), 23);
+
+    for (auto it = quests.begin(); it != quests.end(); ++it)
+        data.WriteBits(it->second.size(), 24);
+
+    for (auto it = quests.begin(); it != quests.end(); ++it)
+    {
+        data << uint32(it->first);
+        for (const auto& entry : it->second)
+            data << uint32(entry);
+    }
+
+    SendPacket(&data);
+}
+
 void WorldSession::HandleQuestPOIQuery(WorldPacket& recvData)
 {
     uint32 count;