Implement requestAnimationFrame for web (#1519)

* Use requestAnimationFrame for polling wasm

* Implement `requestAnimationFrame` for stdweb

Co-authored-by: Ryan G <ryanisaacg@users.noreply.github.com>

src/platform_impl/web/event_loop/runner.rs

@@ -241,7 +241,7 @@ impl<T: 'static> Shared<T> {
             root::ControlFlow::Poll => {
                 let cloned = self.clone();
                 State::Poll {
-                    timeout: backend::Timeout::new(move || cloned.poll(), Duration::from_millis(0)),
+                    request: backend::AnimationFrameRequest::new(move || cloned.poll()),
                 }
             }
             root::ControlFlow::Wait => State::Wait {

src/platform_impl/web/event_loop/state.rs

@@ -15,7 +15,7 @@ pub enum State {
         start: Instant,
     },
     Poll {
-        timeout: backend::Timeout,
+        request: backend::AnimationFrameRequest,
     },
     Exit,
 }