Add Iterator.IsField(int, Identifier) method

src/gaemstone.ECS/Iterator.cs

@@ -94,13 +94,14 @@ public unsafe class Iterator
 			return ecs_field_is_set(ptr, index);
 	}
 
+	// TODO: Potentially misleading, doesn't check the field's backing data type.
+	//       The id might be "(Identifier, Name)", but its data type "Identifier".
 	public bool FieldIs<T>(int index)
+		=> FieldIs(index, World.LookupByType<T>());
+	public bool FieldIs(int index, Identifier id)
 	{
-		fixed (ecs_iter_t* ptr = &Value) {
-			var id   = ecs_field_id(ptr, index);
-			var comp = World.LookupByTypeOrThrow<T>();
-			return id == comp.Entity.Value.Data;
-		}
+		fixed (ecs_iter_t* ptr = &Value)
+			return ecs_field_id(ptr, index) == id.Value;
 	}
 
 	public override string ToString()