Add set_attribute API for MountedData API

[wheregmis]

Feature Request

onmounted: move |evt|{
 let element = Some(cx.data())
 // Currently, the MountedData API provides methods like `set_focus()` and `scroll_to()` for manipulating mounted elements, but lacks the ability to directly modify element styles after mounting.
}

If i want this to work on web i can do, but we dont have cross platform api to do this

       let test = element.try_as_web_event().unwrap();

        test.set_attribute("style", style).unwrap();