[Quest API] Add IsRareSpawn() to Perl/Lua. (#2338)

- Add $npc->IsRareSpawn() to Perl.
- Add npc:IsRareSpawn() to Lua.

zone/npc.h

@@ -488,6 +488,7 @@ public:
 	void	SetHeroForgeModel(uint32 model) { herosforgemodel = model; }
 
 	bool IsRaidTarget() const { return raid_target; };
+	bool IsRareSpawn() const { return rare_spawn; }
 	void ResetHPUpdateTimer() { send_hp_update_timer.Start(); }
 
 	bool IgnoreDespawn() { return ignore_despawn; }