[Expeditions] Cleanup client dz safe return methods (#1300)

This changes Zone::GetDynamicZone to return a pointer instead of a copy
and also lets DynamicZone be forward declared in zone.h

zone/zone.h

@@ -33,10 +33,11 @@
 #include "spawn2.h"
 #include "spawngroup.h"
 #include "aa_ability.h"
-#include "dynamic_zone.h"
 #include "pathfinder_interface.h"
 #include "global_loot_manager.h"
 
+class DynamicZone;
+
 struct ZonePoint {
 	float  x;
 	float  y;
@@ -178,7 +179,7 @@ public:
 	void DumpMerchantList(uint32 npcid);
 	int SaveTempItem(uint32 merchantid, uint32 npcid, uint32 item, int32 charges, bool sold = false);
 	int32 MobsAggroCount() { return aggroedmobs; }
-	DynamicZone GetDynamicZone();
+	DynamicZone* GetDynamicZone();
 
 	IPathfinder                                   *pathing;
 	LinkedList<NPC_Emote_Struct *>                NPCEmoteList;