feat: 添加默认居中适配

Author: BrokenMyth

Runtime/FairyGUIFormHelper.cs

@@ -88,6 +88,8 @@ public override IUIForm CreateUIForm(object uiFormInstance, Type uiFormType, obj
             }
 
             uiGroupComponent.AddChild(component);
+            component.x = (uiGroupComponent.width - component.width) / 2f;
+            component.y = (uiGroupComponent.height - component.height) / 2f;
             return uiForm;
         }