Core/Scripts: dynamic_spawning follow-up, I had forgotten JustRespawned existed.

- Rename JustRespawned to JustAppeared, which better matches its behavior anyway.
- Properly invoke JustAppeared for new (re-)spawns - fixes #20111.
- Fix Thaddius script to work with dynamic_spawning (mostly unrelated to the above) - Feugen/Stalagg should really be a summon group, but I don't have time to fix that right now.
- Fix default value for DynamicEscortNPC to match worldserver.conf.dist.

src/server/game/AI/ScriptedAI/ScriptedEscortAI.cpp

@@ -150,7 +150,7 @@ void npc_escortAI::JustDied(Unit* /*killer*/)
     }
 }
 
-void npc_escortAI::JustRespawned()
+void npc_escortAI::JustAppeared()
 {
     m_uiEscortState = STATE_ESCORT_NONE;
 

src/server/game/AI/ScriptedAI/ScriptedEscortAI.h

@@ -65,7 +65,7 @@ struct TC_GAME_API npc_escortAI : public ScriptedAI
 
         void JustDied(Unit*) override;
 
-        void JustRespawned() override;
+        void JustAppeared() override;
 
         void ReturnToLastPoint();
 

src/server/game/AI/ScriptedAI/ScriptedFollowerAI.cpp

@@ -145,7 +145,7 @@ void FollowerAI::JustDied(Unit* /*killer*/)
     }
 }
 
-void FollowerAI::JustRespawned()
+void FollowerAI::JustAppeared()
 {
     m_uiFollowState = STATE_FOLLOW_NONE;
 

src/server/game/AI/ScriptedAI/ScriptedFollowerAI.h

@@ -53,7 +53,7 @@ class TC_GAME_API FollowerAI : public ScriptedAI
 
         void JustDied(Unit*) override;
 
-        void JustRespawned() override;
+        void JustAppeared() override;
 
         void UpdateAI(uint32) override;                        //the "internal" update, calls UpdateFollowerAI()
         virtual void UpdateFollowerAI(uint32);        //used when it's needed to add code in update (abilities, scripted events, etc)