[Quest API] Add IsUnderwaterOnly() to Perl/Lua (#2995)

# Perl
- Add `$npc->IsUnderwaterOnly()`.

# Lua
- Add `npc:IsUnderwaterOnly()`.

# Notes
- Allows operators to chec k if an NPC is underwater only.

zone/lua_npc.h

@@ -174,6 +174,7 @@ public:
 	void SetLDoNTrapDetected(bool is_detected);
 	void ScaleNPC(uint8 npc_level);
 	void ScaleNPC(uint8 npc_level, bool override_special_abilities);
+	bool IsUnderwaterOnly();
 	bool HasSpecialAbilities();
 };