Add set_attribute API for MountedData API

## Feature Request

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

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